Matt, I use the Unger Ergotech belt and it's good since it's padded and doesn't cut into you; it's very comfortable.
You could fit any bucket on a belt onto it, but because of its padded size, I reckon it'll only take Unger Ergotech pouches. Even the old green Unger pouches wouldn't fit, and if they did, they'd look strange I think.
The Ergotech pouches are very good too. Nice and big with a handy velcro pocket on the side.
I wouldn't buy the shoulder staps though. You need to be a rocket scientist to fit them to the belt. I couldn't work out how to fit them; no instructions; and I'm an ex squaddie whose used to 'belt kits'. Mine are hidden under the stairs somewhere.
Also, I find all window cleaning belt kits a pain to adjust the size of the belt, particularly this time of year when you want to wear a fleece, and when you get warmer, downsize to a polo shirt.
It's a pain to re-adjust the belt size; so you either have it too tight when you're wearing a fleece or too loose when wearing a polo shirt.
I'm sure there's a better way.