I have the red LED tailcap from for the WE M90. It has 4 leds, nothing fancy. It's mostly flood, pretty dim, but can light up a dark room just fine to see around. It looks like 5mm LEDs and no reflector. It's a twisty, but I found that if you twist it down right before it turns on, you can depress the tailcap and get a momentary feature (for the main and tail light). BTW, It's probably not recommended to do this, since it is a twisty afterall.
Overall, it's a nice feature, but I prefer the clicky tailcap that comes stock since I already have a backup light with another set of batteries. It's good if you carry just one light I suppose, but who on CPF does just the bare minimum.
Also, the LED tailcap is a tad fatter than the clicky tailcap.