It all depends on the school.
My eldest went to a small school that was run by a HG+ person. The school was aimed at gifted kids, but didn't restrict itself to them. It was very small and very flexible, and we only left because he sold it to a person who told him she wouldn't change it --- and then changed it. She destroyed it and more than half the families left. It was awful.
But before that, it was superb.
In my meandering experience, smaller schools are more flexible, as are schools that are run by gifted people.
The thing about schools for gifted kids is that most of them (not all!) define gifted in a relatively broad way (e.g. IQ cutoff of 125). The schools are facing a reality, which is that restricting themselves to HG+ kids would limit them to <1% of kids. This model might not be sustainable outside of a large urban area.
So this means that there are a lot of gifted schools that may be great for kids with IQs in the 95th-99th percentile range, but decreasingly so as ability levels go farther past the 99th percentile. I've read a number of posts on this forum from people saying things along the lines of "even the local school for gifted kids couldn't do anything for our child."
In all honesty, and this a bit OT, I think that giftedness and levels of giftedness are very poorly understood right now, which contributes to the problem. Ruf's book is anecdotal, and I haven't seen a really good publication that digs deep and tries to characterize gifted people.