Ds has one, but it hasn't been very successful. They are very expensive to make, and it took 3 goes to get our right (the measuring is very difficult - I down loaded a video he had never seen to keep him entertained, but it still had to be remeasured!) so you will only get one. Ds's was made in red and blue to look like spiderman!
Ds wore his well for the first week and then just resisted any attempts to get it on. It is quite hard to get it on, as it is so tight, ds hates sips and there are zips on the legs (which we needed to undo to change nappies) Ds loves deep pressure and being squeezed, so we thought he would love the sensation, but he just didn't.
Ds's physio said that with some children they just work, and you know they are working because the child is happy to put them on, and they clearly feel the difference (ds is like this with his splints, he doesn't mind wearing them because his feet don't hurt, and he doesn't wobble so much). Other children she said, the battle to get it on just doesn't seem worth 'the reward' - ie better sitting and sensory feedback. Basically ds just wants to flop, and if he wants feedback he climbs all over one of us until we squash him!!
Ds has problems with temperature control, so we were concerned about him getting to hot, but this didn't actually seem to be an issue.
There were a few concerns about ds's chest, before having the suit as it is very tight on the chest so considering your ds's asthma, it might be worth just double checking with about this.
It washes and dries really quickly. and is un-noticeable under clothes.
I can take a photo of it later (minus ds!) so you can see what it is like - ds's is a short leg and arm suit that looks like a wetsuit.