I love my HAB. It has saved my sanity. Maya can be quite gassy and impossible to settle at times. But within a couple of minutes in the HAB, she's fast asleep. Quite amazing, really. Sometimes I walk around for an hour with no success and then I put her in the HAb and it's instant. Couldn't live without it. She's only 2 months old, so I haven't had the issue of summer heat. But it does get quite cozy. I usually only wear a thin long-sleeved shirt underneath. I'd imagine you wouldn't need to wear much in summer. It takes a few tries to get the hang of tying it, but then it's no problem.
So, I second Gill's comment, it's worth every cent.
Am looking at getting the ergo too for ease of use.