For me the best answer was from khris that whatever you buy there are only 2 ways - it's good player or it's - potato. If he is that second option than you should get rid of him as soon as possible.
2 seasons ago i had goalkeeper 6* with one on one stopper and he was really bad, usually get 6 rating at the end of the match. Than next season i bought other 5* without any special ability and he is much much better. He gets often 8 rating, he saves a lot of goals. Plus i make him as corner kick taker and he is really good at this ( i know how it sound so ridiculous and nordeus must change this because it is total nosense).