Don't know much other than what I've read online. I've seen some go for cheaper that have been barely used on a FB swap page.
Reviews that I've read have said that it's fine up to 20-25 lbs for 30-45 minutes (though I will say I haven't ran across a comment saying they've used it with a much bigger kid). It's like an unpadded mei tai, only with buckles instead of long straps. The nylon does not really make it cooler than say cotton, but then again you're still wearing a little mini heater. It's not meant to be a full time SSC, but more of an extra just in case traveling carrier. Probably why I've seen them on swap already - people bought them hoping to be the SSC for them but it's meant for for a lightweight, small extra carrier that one can easily keep on them when they're not planning on a lot or any BWing.
I kid you not, I was just researching this thing. There are some local moms singing it's praises saying they wear with this one for 6+ hours and it's great. One said she has a bad back and is very petite and she wore her 18month old for 5 hours at an event and wasn't even sore. Since she is local, and it's been around 105* consistently here, I was looking into it. I can't afford to buy literally ANYTHING right now though, and I couldn't find any that were cheap anywhere.
I'm with you Leigh, in that it would be nice to have a carrier that is REALLY that small to just have on hand in your bag just in case. We have it happen SO often these days that we don't have a carrier when we want one (because we didn't want to lug one of ours around) or we bring one and don't end up using it, and then resent the fact that we have to lug it around.