I can only speak for this one -- it's an early-college program, that recently expanded to middle school from just high school. So the idea is to do way more in a shorter time, which means more homework.
The person who is urging her to attend absolutely loves it, it works for him. And as he talks about how awesome it is I keep having "SHOULD I send her there??" pangs. But as awesome as it seems, I just am not comfortable with such an all-encompassing focus on academics at this age. And by the time sozlet gets to high school, her current school system has many early-college options too (AP but other stuff as well).
And making the whole decision not really a decision is the fact that sozlet doesn't want to go, at all. She gets why he likes it and she's happy for him but she's very happy where she is. She's doing algebra this year with the 8th-graders and has some really good (new) gifted program teachers and she's getting what she needs out of school. Plus sports and friends and all the rest of it. (The STEM school is just plain school, no extracurriculars.)