Have four, I think, different types, buried in the drawer that stuff goes into that you probably will never use again, but don't want to toss out.
They are faster than doing the job by hand, but find that they make the shrimp look a bit shaggy.
They give a better presentation if used before you cook the shrimp, but I always cook them in the shell and then devein.
Have gone back to using the hand shelling method and deveining with a sharp knife. And always buy the biggest shrimp I can because the fewer shrimp I have to shell and devein the better.
But as SpiceUmUp said, these gizmos are cheap (don't think I've spent more than 2 or 3 bucks for one) and would probably suggest giving one a try. The curved aluminum one seems to work the best as I recall. There are some plastic ones that have a bulbous end that you shove into the intestine which I do not like at all.
Doubt this helps much, but that's my humble opinion.