I use the C5L for my EDC Steyr C9. I endorse it fully. The Zombie edition simply has the green biohazard symbol on it. The X5l will serve you also, but for me I went with the C5L because it is more compact. I have only had a few "problems" with it since I got it, mainly with the buttons pressing/turning on to the "right" setting. (As in it seemed to change them itself) It hasn't been a nuisance or anything for me, I just tapped it and it went right back to what it was supposed to be doing.
Viridian is my personal choice for a laser, being green is easier to see. They are also now breaking into the red laser market, just to stay competitive. Now, you want a really fun laser, totally not able to be put on a firearm, look at "Wicked Lasers"...they are awesome, expensive toys. Ahh, wishlists...