These have been on e bay for a long time now. There are definitely some slight differences between the older style Phoenix straps and the newer ones.

In my experience, the non etched buckle versions are shorter and can suit smaller wrists.

£100 isn’t actually that expensive for what is a proven “not modern” Phoenix strap.

For example, there is a well known strap collector who is currently selling NOS 90s Phoenix straps for multiples of the asking price of the straps you posted.

Some people are really into their straps and some are t.