Tax avoidance is perfectly legal though. The use of pensions, ISAs and some salary sacrifice arrangements are all legitimate ways of avoding tax!
I imagine that there'll be a fair amount of AI / data analytics used anyway, much as they already use software to pick up any inconsistencies on taxpayer data that could point to tax evasion.
HMRC also already has has a shared service to check bank account details are correct, and other government departments and local authorities ca also collect bank details and checl them with the shared service. They can't, without a court order I don't think, actually access the transaction level detail.
But given taxpayers are already subject to scrutiny, I don't see why benefit claimants shoud be exempt, and I think it's reasonable to make sure that those claiming are entitled to do so.