OK, my first post but I've seen this question asked several times here and hope to clear things up once and for all with a valid comparison. I have both a Surefire M910A that I use on patrol and a Rico light that I use in training. For some background, I have been an LEO for 16 years, as a tac-team member and firearms instructor; and am a die-hard Surefire fan (I currently own 11 of their lights). I will say their customer service is second to none. If a part breaks they will send you a new one in days with no questions asked.
On another post here someone stated that "no-one that buys a S/F would buy" a knock-off. Well, I guess I'm the exception. I bought the Rico a little over a year ago (on E-bay) out of curiosity and to preserve my S/F M910A; to keep it from getting dinged and scratched in training. I use the Rico for range-work, scenario training, and Simunitions training, and slap on the M910 for patrol and call-outs.
As a comaprison, at $160.00 plus shipping, I'm impressed with the Rico. It is no cheap toy. It has survived over a year of bumps and knocks, including being dropped twice and taking a .40 SW Sims hit on the side from about 7-10 yards. There is virtually no discernable difference except for the Rico lens being polycarbonate and the S/F being pyrex. The Rico lamp is apparently shock isolated as advertised as it has stood up to repeated full-auto firing from my M4 with no problems. (my M4 is an early model with fixed carry handle and safe/semi/auto lower). The bezel and lamp assebly from the S/F will fit and work in the Rico. When the bulb in the Rico goes, I'll replace it with a S/F MN10 lamp. I can detect no difference in the xenon lamp in brightness or shape between the two. The LEDs on the S/F are brighter however. There is also no noticeable difference in fit on the S/F M73 rail of my M4. The Rico fits as tight as the S/F and the attachment parts appear virtually the same. The vertical grip and polymer frame housing are so similar in fact, that if S/F wasn't known for their "Made in USA" pride, one would swear they were subcontracting Rico to manufacter this part. To sum up, the Rico has withstood a year of hard knocks from me, and this from a true Surefire fan.