Yeah, the horse vacs are quieter. I have never had any problems getting any horse, even our young ones, used to the vacuum. But again, most of our horses are exposed to everything under the sun at our farm imediately. Most of the time they will kinda look at them for a while, but have never had one refuse it. I have had more problems with water hoses than the vacuum.
I used to work at a barn and we used a vaccum on all the show horses. They usually start out scared to death but they grow to love it quickly. It helps to remove alot of dirt that would elsewhere stay close to the skin without a bath, and yes a household vaccum can work as well with the right knozzle
I use a vacuum at the barn. To answer your question, my gelding LOVES the vacuum. He loves the suction feeling, especially on his neck and back. He's 25 and has probably been vacuumed his whole life.
On the other side, my 3 Y/O filly is scared of the vacuum and rears, jumps around, etc. when you try to vacuum her. The first couple times I introduced it to her, she was fine, but when she felt the "sucking" feeling for the first time, she freaked out and broke her cross tie. She's just hot in general, and is 10x worse around clippers. She's the only Morgan I've met who refuses to be vacuumed. The rest of them love it. It doesn't help that she's very sensitive.
Their great in the spring and fall when its too warm for blankets, but wet and muddy.. and the horses love to roll. Trying to get all that caked mud off any other way is crazy! (Which is why, if the filly still doesn' vacuum in a few weeks, she'll be getting a sheet)
I've never used anything other than horse vacuums, but I don't see a problem with others.
The barn I am at has a new boarder who is using one on her horse. One of the old barns I boarded at had a few people who used them. I don't think I would personally use one but they seem to work quite well.