Regular "horse vacuums" are quite common in North America, both the portable and built in models. Generally horses are surprisingly okay with them and many seem to really like them.
I know a few people who have used that "carpet cleaner" and they said the horses don't seem to mind it any more than regular vacuuming but it's somewhat messy to use and the horse is still damp at the end, which is why people would pick something like that over bathing in the first place, so it's not a huge improvement.
it took her 20 mins, it takes me 10 mins to do a filthy horse the old way with a bucket, sponge, shampoo and hose to rinse. i bet it's rubbish on filthy pooey tails too! it was very noisy, i suppose it's good for getting them used to the idea of being clipped etc. hmm, i think i'll stick to the old method.
haha...we had a Henry vaccum at my old yard that we used on the horses! Some of them absolutely love it, whilst others are understandably seriously freaked out by it!!
The "selling point" is as an alternative to bathing in cold weather. Unless you have a heated wash stall that's most of the winter in a lot of places!
As I said, though, it still does make the horse damp so you still need an above freezing barn and a collection of coolers. I'm also told it works very well on dusty horses - again, not something one has to worry about very often here.