So in the end I did get an offer after all. It came via the agency and it’s only verbal at the moment but it should all be formalised in the next few days.
The technology confusion resolved itself fine (she was actually thinking of something else), so that pretty much took away my reservations.
It’s a good salary bump too so I’m happy. It’ll be a more senior role than I’m doing at the moment. Overall it’s feeling like a good career move and I’m not going to fish for a counter offer after all.