I don’t know anything about those colleges but I do have some EHCP experience I will share...
Dd has been out of school since half way through year 10 - she has ADHD, ASD (high functioning) and mental health issues (self harm, anorexia, overdoses, suicidal thoughts, anxiety). For a significant amount of time she has been an in patient in an adolescent mental health unit and she took 7 GCSEs in hospital school, she is very bright and got them all at high grades. With some additional support from the EHCP and after significant research into which local school would be best on my part, she returned to mainstream school to start A Levels last September. She could not cope in that environment at all and the support was nowhere near enough (they did try their best!) and it ended in a 5 month hospital admission. As I said above, she will be attending West Heath and Sackville in September with a lot of support including transport, delivered under the EHCP at significant expense. When the application went to the panel, it was agreed first time and I understand that one of the reasons they agreed quickly (these placements being difficult to get funding for) was because a return to mainstream school had been tried and ended badly - if we had not already done so, we would have had to try a mainstream school first.
In your position, I would want every detail of the support those colleges offer and I would be measuring it against DDs needs. If you feel Unstead Park is the best or only fit I would be making the case to the EHCP officer/appealing/doing whatever is necessary!
Alternatively, would online school be an option? We were in touch with InterHigh and were quite impressed but dd doesn’t want to be home alone and wouldn’t use their online commonroom facility.
Lots of sympathy - there seem to be a good number of schools for those with ASD who need life and independence skills and so few for those who are academically able but can’t cope in mainstream.