In reply to mutt:
I bought the Red Chilli one because I was sick of not trying boulder problems that involved a knee and didn't own a kneepad, but figured that I wasn't going to get that into knees so might as well spend half the cash. I had a year or so of using it on and off and managed a couple of things where a kneescum makes things slightly easier, but found that when the knee was obligatory or the hard bit I got completely shut down, and concluded that I was just terrible at knees. I also found that the elastic that connects the straps to the main bulk of the pad started falling apart bizarrely quickly, to the point where I had to be quite careful putting it on and taking it off.
The first time I borrowed a mate's Send pad I did a move that I'd spent the previous two hours not managing in the Red Chilli one, and since buying one have had a great time realising that, while there is a skill to using knees, there's also an element of not having totally shit rubber (and build quality). Basically the Red Chilli one protects your thigh from abrasion and means that you can experiment a bit and do some token kneebarring, but for actually sticking to the rock on anything other than an absolute sinker knee it's crap.