'I am more concerned about stand alone academies.'
There are different problems but the whole model of academies, whether chains or standalone, is a problem. Looking at the number of schools judged inadequate, there's a greater proportion of sponsored academies than of community schools (if I've counted/filtered correctly on the performance tables) and there is a worrying number of converter academies, despite the fact that most were good outstanding to begin with.
36 sponsored academies out of 404 (9%)
34 foundation schools out of 565 (6%)
52 community schools out of 1158 (4%)
13 converter academies out of 1200/381 inspected (1%/3%)
9 voluntary aided schools out of 442 (2%)
Some of the inadequate sponsored academies are standalone schools and some of the converter academies have sponsors (e.g. the Ormiston ones) but neither the league tables nor Edubase are transparent about who the sponsors are, unless the school has been rebranded with the name of a chain. There can also be many complicated co-sponsor arrangements.
One-off academies and foundation schools (of which many are secondary moderns) are, as you suggest prh47bridge, really vulnerable. The statistics prove to me that those schools with the back-up of a local authority and/or diocese are the safest.
With AET, it may be an advantage for some schools that it takes a hands-off approach if there is strong representation from the local community, but equally it hasn't been effective improvement partner in the case of three schools judged inadequate. Who is picking up the pieces at East Point Academy and Sandown Bay now they are back in special measures? Has AET been allowed to continue there while community schools are forcibly academised? Other chains that are more hands-on give less autonomy to individual schools than even LA maintained schools enjoy and override local concerns.
At the same time, a local authority is no longer able to plan for demographic changes or to even attempt to iron out inequalities in admissions.
Quite apart from any possible financial irregularities I don't see the benefits of academy status for school improvement either and can only see wastage and inflexibility. The outstanding converter academies were mostly outstanding previously (or would have been on their next inspection). The outstanding sponsored academies were seldom schools previously in special measures - they had either started that improvement prior to conversion and received rebuilding grants with the sponsor or were new schools (Mossbourne) starting with a new head, new building, new admissions policy.