I have one .45 kit, I've used it and it works
just fine. I do prefer shooting the gun in 9mm, particularly using the +P+ Hirtenberger ammo, but it's nice to have a choice of calibers depending on ammo availability.
The .22 kit provides for real cheap shooting and is also a good way to get a child or woman into shooting without the action of the larger calibers.
My .45 kit worked flawlessly right out of the box, and I have two more on the way, to be put away for sale with my other Uzis in the future. Biggest drawback is the 16 round mag...it runs out too fast.
I dare say, that if you like .45, you won't be disappointed.
Pretty sure that if you get a Grease gun conversion lower, you can use the same bolt and barrel, but use Greasegun mags which are very inexpensive now.