I think the MicroFire F6L is basically a $60 regulated 3W LED bulb assembly in a $30 host body (Note: those are the public retail prices taken from the Pacific Tactical Solutions public website
http://www.pts-flashlights.com, if you create an account there and contact CPF member Mike@PTS you will get a special CPF member discount rate that is typically 5-15% lower).
If you already have a SureFire-type light that you like, you might as well just get the F6L bulb assembly, since there is nothing particularly special about the F6L body (unless you want the clickie tailswitch, which is a normal clickie rather than a reverse-clickie, which I know will please some people). The F6L body construction is better than the 'Golston 7w' or the '7W Super Bright, 3.7V x2', but is not quite as nice as a SureFire. On my example, the body tube is a slightly different shade of black than the head and tail (the body is a bit more flat, while the head and tail are slightly glossier). I'm not sure if this is intentional for grip or for looks (it looks nice that way, since the head and tail match) or if it is just a coincidence due to parts being annodized in different batches.
If you are thinking about getting a MicroFire F6L, it might be worth considering getting a Wolf Eyes 6T (currently an excellent deal over at PTS if you have the CPF discount rate) and installing the F6L bulb in that host. Personally, I think this is what I'd do if I wanted to buy another one right now, since it doesn't cost that much more (with the current special price on the Wolf Eyes 6T) and gives you the LED tailcap of the 6T and a spare incandescent bulb.
The F6L bulb assembly might also make a very good backup bulb for a light that normally uses a 6-9V incandescent lamp. Since it is shock resistant and won't burn out, it should be an excellent backup.
The strong points of the F6L seem to be the normal clickie switch, the nice spillbeam, runtime (advertised at 100 minutes with extended useful light, on two primaries), 6-9V voltage input range, and the ability to use the bulb in a number of different host bodies. This means you have several options for battery configurations, based on your needs. It would be interesting to use the F6L bulb in a four cell body with two 18650's; the runtime ought to be impressive.
If you are looking for a super-bright light or lots of throw, I think you'd be disappointed by the F6L and I would recommend the M2L instead. The M2L is a two-stage Lux-V that is very bright, however it is also significantly more expensive than the F6L and is a bit too bulky to comfortably drop in a pocket.
So that's my opinion on the MicroFire F6L.