I replaced the core and o-rings a couple of years ago - was either Allmakes or Britpart, somewhere I'll have a record of it. The o-rings started dripping again a week or two ago, replaced them yesterday - had a look at the 'end' of the cassette where the core slides in (RHD & only took out dash and ducts, so not a good going over but more of a check for any obvious leaks) and it seems to still be OK. Last time I had the heater box out of it.
Will find out after a proper run, it's 80% back together for now. It could be my lack of practice with o-ring replacement but it seems from that one sample that the cheaper core might be able to outlast them - and as both need at least most of the dash out to me that indicates there's not a huge benefit to getting an expensive version.
If I were totally confident that I can fit o-rings left right and centre then I'd probably get the Audi/equivalent core and do it. I don't mind the dash coming out except for the fact that most of it falls apart a bit more each time.