+1 to all grumpy says. They can be an implement of destruction, when wrongly used.
In addition, I'd like to say that in general, it's not a good idea to use a rattle gun for doing up fasteners. Getting stubborn ones undone is their best use, in repair and maintenance.
There are rare exceptions, like running the nuts up Victa full crank 2-stroke crankcase studs [which is a very slow job to do with a hand ratchet], but not that many.
Yes, production lines use them to run up and final tighten. But the rattle guns used there are hardware torque limited, for the specific fastener type and position on the assembly.
Some years back, a mob called 'Pete's Bargains' in Ringwood, Vic had a lot of ex-Nissan production rattle guns for sale, after Nissan closed down their Oz assembly plant. They were very cheap, but not very useful for general workshop use, due to the fixed torque limiters.
Repco's house brand pneumatic gear was decent quality then, and I could wangle their top trade discount, so I bought a few of those instead.
