Sorry, a little late to the party here. I saw this thread originally and thought that the Surefire was out of the question. Anyway, yes, I LOVE mine. They are quite pricey, but they are worth the money if you don't mind spending that much. They are VERY solid (as in you could almost beat someone to death with one). They do have a little heft to them due to the metal internal frame, which will add a little weight to the front of your gun (although, depending on where you mount it, it balances nicely). The M900 has the main light which can be activated either by the tape switches on the grip for momentary activation or the flip/knob switch for constant "on" use. There is also a "thumb" switch at the rear of the unit that activates the two low power LED's (which are available in red, white, or blue. Mine are blue). The LED's are referred to as "Navigation Lights". These are nice if you don't want to kick on the VERY bright main light, and they will still preserve a degree of your own adjusted natural "night vision". (Ya know, when your eyes acclimate to the darkness). The Surefires are available with 2 different attachment points. Either an ARMS throw lever or thumbscrews. (The M900 has ARMS, the M910 has thumbscrews). Mine is the M900.
Now, be VERY VERY careful buying a used one. There is an airsoft company that puts one out that has RICOH stamped on the side (and I'm sure there are a few others crapping out knock-offs at this point as well). The Surefire lights will have their logo on them. The airsoft shat will not hold up to real use, especially recoil. If you found one on Craigslist, check it out as best you can. If it is indeed a Surefire and they are asking a reasonable price, I would recommend that you jump on it. I absolutely love mine.
I'll keep a better eye on this thread, so if you have any questions, please ask.
I'll see if I can't get some better close ups of it tonight. But here is one shot of it.

By the way, the light pictured in the Craigslist ad does appear to be a Surefire based on the logos, but as plea pointed out, it's an M910, not an M900. (Thumbscrews).