I was looking for a compact green laser & light combo for my IWB EDC H & K VP9. Here's my take and why I chose the Crimson Trace Rail Master Pro over the very good Viridian C5L & the very good Streamlight TLR-4G (which I also own). The Crimson Trace has replaced the larger TLR-4G.
1) When it comes to the green laser, it's a wash between the 3 units. All are great. The Viridian's green laser does not have the ever so slight hint of a blue tint in the green when compared to the other 2.
2) If brightness of the tactical light and not compactness of the unit is more important to you, go with the TLR-4G.
3) All 3 have good ergonomic laser & tac light controls for myself. Your personal preference may vary. Again, this is a wash in my book.
4) All 3 are easy to attached to my VP9's rail, and all 3 seem to be robust while on my pistol (no wimps here). This is another wash between the 3. However, the TLR-4G is the easiest for "quick on & off,"
5) I do prefer the housing design of the Crimson Trace over the Viridian. Along with fewer angles designed in to housing, the tactical light lens, the laser, and the sight adjustment screws are all recessed further into said housing. I believe this design may do a better job of protection in the long run. This not an issue when cleaning of the lenses is necessary.
6) Here's a simple thing; I appreciate the design of the supplied laser's screw adjustment wrench. It is slightly longer than others I've seen, and has a nice fob on the end for ...