Well, the big picture answer is "not much" since as mentioned, you sacrifice so much velocity, and you still get a lot of cylinder gap blast with nothing really to show for it. But whatever butters your bread - why not if it's what you want? I'd want a 6" bbl minimum on a .17 hummer revolver personally.
And it likely IS "worth it" or almost, on the open market, even if not worth it to you or me. Along those lines, I just ended up with in trade, then sold, a gun which has got to be the most useless piece of junk on the face of the planet - a GSG MP5 clone in .22lr - the pistol version - pot metal junk, yet huge and heavy, unreliable & inaccurate (by most accounts), un-concealable, un-shoulder-able, un-scope-able (as is from the factory) -- worthless - and yet amazingly, I found a 20-something dude who collects them and wanted it. These are pure, unmitigated Umarex dungheaps, yet have a following, just because they look like an MP5 and are made in Deutchland, I suppose. I wouldn't give a squirt of fluid for one, but to each his own. I could get two Phoenix HP-22 pistols and have almost $100 left over, for what this guy paid for that steaming heap, and have two small concealable .22 pistols which are just as accurate and more reliable than that GSG - sorry, just venting. At least I didn't get stuck with it - gotta be more careful on my trade deals.