I have both a SouthOrd pick gun, and a few homemade snap picks. My experienced have been that the homemade snap picks - even the ones made from coat hanger - tend to work even better than the SouthOrd gun. I hardly use either of them anymore, except in demonstration (where nothing ever works

) but if I were in a pinch and couldn't trust my manual picking skills, I'd actually prefer to have the snap pick (yes, even the coat hanger one) over the pick gun.
The only significant downside to the snap pick is, as mentioned previously, comfort. If you use one of these for any length of time it has the tendancy to make you want to rip out your toenails with plyers to mask the pain in the fleshy part of your thumb. But that's a small price to pay, right?

Actually, in practical use you probably wouldn't need to snap it nearly enough times to make your thumb soar, so it's actually quite a practical little tool. I simply don't use one because they're no fun.
I think that a more likely reason you're apt to see a professional lockie carrying a pro pick gun is that of image. I would be a bit embarrassed if I were a lockie and I showed up with a coat hanger pick gun, snapped it in the lock a couple times, and then asked for my $50.

Not to mention I'd be a bit worried that I'd never get another call from that customer.
Hope this helps.
db