@11minus is your prep under the umbrella of Dukes Education by any chance? Hence the recommendation of Eaton Square which is part of Dukes?
Eaton Square doesn’t have that much of a track record, having only been started up in (I think) 2017 as a private equity venture. I’m not sure what is the source of the prestige your head is referring to, or whether that’s something that’s important to you.
Depending on location you might well find Sutton High worth a phone call, as a PP mentioned. It has a lovely ethos. And your fees wouldn’t be heading into the pockets of private equity profiteers!