You can put a second o-ring on the C3's tail end, just like the M3 has. You can also put the shock isolated M2 bezel (13586-1 is HA and 13586-11 is black) on it, and have shock isolation for the lamp assembly. I really like the utility of the pocket clip on the C3. The lanyard and lanyard ring can be purchased separately, if you need it. As for looks, beauty is in the eyes of the beholder. I have the M3, M3T and several C3's. Love them all. All of my C2's and C3's get the second o-ring as soon as the box is opened. I've got a 13586-11 on a 9P, but am thinking of putting it on a C2-BK. Also have a KT1-HA Turbo Head that floats around my collection. It's on an E2O at the moment. I highly recommend the Surefire C3. Feel the same about the M3. Just can't afford to buy any more M3's.
I don't recommend buying any Surefire with the Lexan lens. The only exception would be if you want a 9P or D3 for a Lego project. I guess what I am trying to say is, the C2-C3 and G2Z are the cheapest, classic size Surefires, that I would recommend, for use as is.
oldgrandpajack
PS: I apologize for steering anyone the wrong way with misinformation. I have corrected this post. Thanks to Chamenos, it is now correct.
The last O-ring on the tail is part number 19-01-077. The first O-ring (already installed) on the tail is the standard 19-01-040. This is also from Chamenos. Thank you, Chamenos!