The viridian laser is a good value for 150 bucks. It is big but is a good laser. If you can afford the 150 and feel you need a laser then the viridian for teh SR9 is a good value and probably the least expensive good quality laser you will find for the gun. There may be cheaper ones out there but they are mostly pointers with clamps on them.
finally got my SR9...
Check this out