I've never seen this one before, but it looks like a copy of the regular album. The track listing is the same, and the running times match the CD to within a few seconds.
The Teaser Tape, a promo which contains short edits of each song, has a different running order and obviously a much shorter running time.
I guess it's possible this tape has some different material, but I am not sure I would spend £50 to find out.
Looks suspicious to me. I'd ask the seller to do a digital transfer and post the audio online. If it turns out to be something unusual (or even if it doesn't), a true collector wouldn't see a digital version as lessening the value of the cassette itself, so it'd still sell. Nobody should ever have to spend money to get a sample of what something sounds like.
This is actually what it purports to be. It's the 80s version of the CD-R promos that are used now. Actually not that rare on eBay, but they always turn up at this sort of price. Kind of expensive for me...