Bump keys (provided the correct tension is used) are very fast, and I've found them to be quite reliable. The disadvantage is that not only can it eventually damage the lock components, but it leaves a permanent mark on the face of the lock unless you take steps to prevent the shoulder of the key from impacting the face of the lock. In my experience, I've bumped a practice lock hundreds and hundreds of times, and they still work fine. I don't buy the whole "it will damage the lock" argument when it comes to pins and springs. I'm sure it CAN, and probably has happened. But I think it would typically take a lot of bumping to damage it. It will however, damage the face of the lock. Some people cut the shoulder back and put a dollop of hot glue on it, some people use a rubber o-ring to prevent this, but I never have bothered. Another disadvantage is you need one key for each type of lock. There isn't a universal bump key.
Here is one of my practice bump locks. You can see the damage above the keyway. However, a couple of bumps will only do some minimal damage. This one has seen hundreds, if not thousands of bumps.
Personally, I've never had great success with pick guns; both manual or electric. I'm sure it's because I don't practice enough. I know other people who use one religiously. It's typically easier for me just to use a rake at a lock-out. The advantages are that it's universal, and if you are good with it, pretty quick. Like bumping, it does take a toll on the pins, but it doesn't mar the face of the lock. And it looks cool to a customer.
On the other hand, I have sold high-security locks to customers who watched me bump open their lock. However, 99% of the time, I won't use a bump-key unless I'm having issues picking and raking.
As for sound, commercial pick guns aren't quiet. They have a loud "click," which is about the same noise level as a bump hammer makes. I've never used a homemade pick-gun, but they may be quieter.
As discussed in other posts, there can be an issue when it comes to billing a customer if you open their lock in 3 seconds with a single bump. People often don't want to pay the normal rate since it was "so easy" to get them in. They commonly think it shouldn't cost very much since it only took a couple seconds. That can be an issue. Of course, they don't want to pay more if it takes you a long time since they expect you to be "better" at your job. But that's another issue for another post. I bring it up here because it can be a disadvantage when it comes to locksmith field work.
