I have each frame size now and intend to purchase the caliber conversions for each.
Do they still offer conversion kits for the small frame guns? I thought that was discontinued when the discontinued offering the small frame guns.
For more recent models of the small frame guns, to convert from .40 to 9, all you need to do is buy their barrel. Some of the later model small frame gunss were built from the factory to be compatible; the .40 and 9mm guns had the same diameter barrels (and openings in the slide). Some of the early 9mms, before they began building .40 models, might not accept a .40 barrel.
I don't think I've run into a .22 kit for the small-frame Witness, but I'm pretty sure they're out there. Nothing from CZ, however, works. Witnesses look like CZ clones, but they're not clones in the true sense of the term.
I have had a bunch of Witnesses, but they were all bought used, so the only interactions I've had with Customer Service was to order parts -- and that has been fine. I had a nice .45 Sport Long Slide, but the barrel failed, and later the SuperSight broke and had to be replaced. Those weren't warranty issues, as the guns were used, but it was both aggravating and costly. Great gun, otherwise. All of my other Witnesses have been very good guns.
Were it not for the large number of horror stories about Customer Service (for warranty-covered guns) I've heard over the past 10 years, I would have bought one of their nicer large-frame guns; they have impressive features and generally great triggers, out of the box: the Elite or Pro guns...
In the past, it wasn't just that they wouldn't honor warranties on some problems, in many cases, they wouldn't even talk with the owner about the gun, immediately accused them of things they had no way of substantiating (sight unseen), and they often would refuse to even examine the gun. That was terrible customer service, and I found it offputting. It's going to take several years of good comments before I trust them.