They are very good. I've been wearing the ASO braces for the last few years now and am quite happy with them. The ASO brace is also very popular among NBA players who are probably at most risk to sprain their ankles. I've seen everyone from Lebron James, Ray Allen, Chauncy Billups, to Dwyane Wade wearing these.
Regarding the sizing issue. I'm not sure. My foot is extremely narrow so the braces in a sense serve more than one purpose for me.