~ This review will be used for both the SL5 (1AA) and SL6 (2x123,1x18650) versions of the Spark Lights ~

First Impressions:
    The first thing that you will notice about the Spark SL6 is its small size for an 18650 compatible light, especially considering that it has a tail switch and a side switch. Most lights with a side switch end up adding a good bit of length to the light. The second thing is that, like all the Spark lights, its anodized finish is much duller than others, I happen to like this as its something different and feels less slick in your hand, especially with wet hands. I personally think the SL6 is of the best looking lights I have seen out so far. I love the fluting grooves on the head, the way body is designed, just seems to have more going on style wise than other lights. Then as soon as I turned it on I knew I was going to love it for EDC. The beam has a much wider hotspot than most, that fades out nicely to the spill. I personally like this type of beam for a EDC light. I have other larger lights if I want tight long distance throw beams.

Size/Weight:
    As I said above, I really think Spark did an excellent job of keeping down the bulk on this light. No its not the smallest 2x123 1x18650 cell light out there, but its definitely toward the small end. The fact that they kept it small even though it has a side switch is impressive. The SL5 is the 1AA version and the same goes with it also, they did a great job of keeping the light small. Both are also quite light weight in your hand.

Grip/Handling:
    There is not alot of knurling on the SL6 but I still find it easy to keep a nice grip on. Part of that is due to the dull finish and the overall shape of it. I found it fit my hand very well and each of the two switches were very easy to access and operate.... alittle too easy. Here lies the problem. You HAVE to lock out the light to pocket carry it. The side switch is very easy to accidentally activate. I tried carrying it for several weeks with out locking it out, and several times the light accidentally turned on in my pocket. Once it was extremely hot when I pulled it out of my pocket. Not hot enough to burn me, but almost hot enough that I couldn't comfortably hold the head. This was a huge disappointment to me. I still EDC this light, but its a shame that it has to be locked out, it makes deploying it a bit slower and cumbersome. The light fits my EDC needs perfectly in every other way, so I am excepting this tradeoff for now. I would like to see Spark make the side switch stiffer, maybe with more of a distinct click, and recess it alot more.
A more distinct click would also help give it some tactile feedback. Every so often I find I have pressed the switch alittle too lightly and not activated the light.
    The switch on the SL5 is a bit smaller and there was not as high of a risk of accidentally activating it, but it is still a problem and something you should watch out for.

Build Quality:
    So far I own 3 Spark lights, including the ST6 Headlamp, and I see no problems with the build quality of these lights. The machining is quite good, but they do have a bit of a sharp feel on the grooves and the ends of the light. Its not that they are poorly machined or actually sharp, they just aren't rounded at all in some places. The threading can feel slightly rough when turning the tailcaps due to the dull anodizing finish, but I don't see it being a problem.
    The SL6 pocket clip snaps on and can be rotated to any position. This isn't quite as sturdy as some other permanent mounting solutions but I have not had any issues with it accidentally moving or coming off.

Features:
    The Spark SL6 has 5 output levels. Both switches operate the light in the same way, a quick press turns the light on or off. While the light is on, pressing and holding a switch will cycle it though its 4 main output levels. At any time the light is on, double clicking the light will activate super mode. I found that double clicking at a medium speed deliberate worked best, and not a real quick double click. I like this interface alot, I like the easy access to super with the double click. Only thing I would like better is adding easy access to low with a triple click.
    Another neat feature that I think is true for most all Spark lights is that you can load the battery in either direction you want. There is no polarity issue. I think this is a nice feature, I could see this being useful when changing the battery in the dark and not having to worry about its orientation.

Output:
     The SL6 has a nice medium to large sized hotspot to its beam that fades out very nicely to the spill light. I personally like this type of beam for a EDC light due to using it mostly for close to medium distances. The SL6 even comes with an optional frosted lens if you want to make the output a pure flood of light with virtually no hotspot at all.
    The SL6 has 5 output levels all together, the highest being Super mode, that is activated by double clicking either of the switches. However, this mode will only stay on for 5 minutes and then step down to high mode. This is a safety feature to protect the led and circuit from overheating. I found that for general use this was not a problem, as I was only using super mode for short durations here and there anyway. I am not sure if the SL5 has this 5 minute limit also.
    Mine is the 800CW version with stands for 800 lumens with a Cool White tinted LED. There is also a Neutral White LED version at slightly less lumens.
    The SL5 also has 5 output levels, however Super mode may not work, or be at a lower output, when using some batteries such as alkaline and nimh. The max rating on Super mode is achieved when using a 14500 rechargeable li-ion cell.
    Both lights have a memory function to remember what mode you were in last, so that when you turn the light back on it will be in the last mode used. However, the SL5 will only remember the mode for a couple minutes if you are not using a 14500 li-ion cell.

Pros:
Easy to operate tail and side switches
Small size for a light with a side and tail switch
Medium hotspot that fades to spill nicely
Great looking design
Reverse Polarity Capable

Cons:
Not designed for long distance throw
Side switch is way too easy to activate, must be locked out (loosen tailcap)
Super mode only last for 5 minutes
Some edges can feel a bit sharp

Conclusion:
    Other than the huge disappointment of having the lockout the light due to the easily activated side switch, I am very pleased with this light and happy that I bought one for my current EDC light. The light feels great in my hand and in actual use having both switches makes the light very easy to use. I really like the larger hotspot that the SL6 has since I will mainly use it for close to medium range. Its nice that super mode at 800 lumens can still reach out a good 80+ yards though when you need it to.