I would buy it if offered, there are only a few around.
Also, the early HW77 rifles are very desirable in themselves, with the 25mm piston and generally high build quality. With a little tuning - or alot, depends what you want to spend - it is the match of any spring rifle made today and can be turned into a PCP-beater. The Tyrolean stock is very comfortable and can help with a consistent hold & accuracy.
The real deal-breaker is THE PRICE. How much is the vendor selling it for? If it is £500 then forget it, £250 and less then it is an OK buy. What can you buy new for £250? Nothing as good as a HW77 Tyrolean.
Even if you bought it and couldn't get on with it, you could resell it on here and it would be gone before you could say 'snap'.