I use it all the time. I'm not sure if I need it, but it's one of the most handy augs for me.
What is the range on the stun gun? I've used the tranq rifle and it annoys me. When I actually want to fire at a long distance, I can't do so from cover and even with the zoom, the shot isn't reliable enough. The silenced sniper rifle seems far more handy to me; I always hit my target, there's a light so I can reliably use it around corners, it's an instant down, and the guys never get back up.