I got one of the first .40S&W P99's and then bought the Laser Devices BA-5 laser for it. I believe that they changed the designation for this unit to BA-6 now but generally it's still the same.
It's a really nice unit and Laser Devices did a good job of keeping the lines of the frame to the laser body. It's very sano and looks a lot better than some cheap pen style laser. Plus it's got the Walther logo on it.
As far a use, I find it's best for dry fire practice. If you've never used a laser before, you will be shocked at just how much you shake just holding the gun. Then try pulling the trigger. Any jerk or pull will be perfectly displayed by the dot.
If you had to shoot from the hip or point shoot, the laser comes in handy because it's a lot faster than an aimed shot. But, I hopefully will never be put in that position. Outside of that it's a nice accessory to my P99 and I view it as somewhat of a collectors item.
-Red-