I knew it wouldn't take long for the negativity to creep in for this kid! For me the obvious answer to this buyback thing is just what Juan said: Bayern have a very cushy right of first refusal. If that's the case, it just means that we see Yesil as a football investment and not a financial one; that we can't turn around and sell him to Barca for £25m in a few years if he turns out to be fantastic. It's a calculated and completely reasonable bet in my opinion.
Also, people worried about the "not ready for the first team" quotes? Seriously? We're paying £1m for an 18-year-old and making no secret of the fact that he's a youth team signing. We've paid a lot more than that in recent years for several youngsters who were much farther from the first team than Yesil is. Sterling, for example, reputedly cost us around £5m including addons when he was 15.
Out of curiosity, can anyone name a transfer in recent memory that did have a clause in which the buying team was literally forced to sell back to the selling team no matter what they wanted? That sort of thing can't be terribly common.