I'm struggling to find stuff not to like, to be honest - at least on paper.
I think the implementation of the LEC structures could be quite challenging - there's a lot of specialist expertise required for that to work. Presumably the specialists would be seconded from the REAs/NEA, but if there is strong demand to set these up then I imagine they'd end up needing quite a few of them.
Edit to add - I just had a look back through the comment chain, so adding some observations.
I don't think that renationalising the power grid is going to be particularly revolutionary. Public ownership of the grid is normal across much of Europe. The proposed structure borrows some bits from the Nordic model, and some bits from the German model (where a lot of utilities are provided by municipal stadtwerke) - they're models that generally work reasonably well. I think that the focus on enabling greater renewables integration through lower costs, cheaper borrowing and greater coordination is overall pretty sensible. And it still leaves the task of developing competitive energy sources to the private sector, which IMHO is better at solving that particular problem.
I think where there may be tensions is when sections of the industry try to lobby for preferential treatment - what happens if a large local employer lobbies the local community to vote on REA budget proposals that favour the employer, but not the decarbonisation strategy?
But, I'm looking for potential flaws. Overall I think this will be perceived by the UK electorate as radical, but in a European context it's not, really.