I have three .22 Hornets at present: an H&R Handirifle, a T/C Encore with a MGM carbine barrel and a Ruger No.3. All shoot very tight groups, at least to the extent that I'm able to shoot.
Two of my Hornets of have improved Kilbourn chambers, while the Ruger is unaltered and waiting until I find a smith I can trust to remove the N.3 barrel to ream it for me. I don't have enough experience yet to say how much difference the improved chamber makes, but I've committed myself to the K Hornet with the other two and prefer them all to share the same brass.
One thing about the Hornet I discovered is that the decapping pin on my Lee universal decapper is too fat to work with my Hornet cases (mostly PPU.) That's only an issue if you decap with one of these -- my regular resize/decap dies don't have this problem. I have both a set of standard Lee Hornet dies plus another set of neck resize dies for the K Hornet.
As with other small-necked .22 cases, loading certain larger grain powders (4227 for example) requires more patience to get the charge loaded without crushing or breaking grains. Otherwise, the Hornet hasn't been any more difficult to load than .223 Rem. I haven't lost any cases to splits or damaged necks so far, but mine are only up to their second or third loadings. My understanding is that case longevity isn't great with the Hornet, and given their thin and comparatively fragile necks I can see how that would be true.
PPU ammo for .22 Hornet used to be
relatively inexpensive, but I bought my supply about 5 years back and I have no ideas about current prices. A quick online check shows brass and loaded ammo in rather short supply right now anyway.
Even if you can't find ammo for it immediately, if you do find a good rifle in .22 Hornet buy it and be patient. Use the ammo shortage as a bargaining point on the price. It's easily one of the most fun centerfire rifle cartridges out there.