Only time will tell, as it often does, but I think it's too simplistic to say it's a case of an unknown quantity against someone 'proven'. You and I aren't exactly avid watchers of Ligue Un, but I'm sure the vast majority of Championship clubs have scouts well acquainted with it. Whilst I appreciate the potential hurdles of getting used to a different football culture etc., it's hardly like the French league is some poor, backwater one - the average quality of player is probably higher than the Championship.
I've said elsewhere, if Madine scores the goals to take you up then £6m is a bargain, but otherwise, it's quite a lot of money for a striker who hasn't ever really been a prolific goalscorer before this season. At 27, he should be coming into his best years as a player, so it could be you're getting him at a good time.
I really don't know enough about Diony to say much, but that Saint Etienne, a club that are usually in the top half of the League, were willing to shell out £9m on him in the summer says something; although that he's not scored this season says something also! I'm comfortable with the arrangement of a loan with a view to buy - it makes it low-risk, but with a potentially massive payoff if he fulfils the potential he showed at Dijon.
I don't know if one can be considered a more 'sure-thing' than the other. Cardiff have signed players like Rickie Lambert and Adam Le Fondre in recent years, who had more pedigree in playing English football than Madine does now, but they weren't successes (we might add Tomlin to that group too?), whilst a punt from the continent in Kenneth Zohore was a bargain - on the flip side, the less said about Andreas Cornelius then better. One thing to Madine's credit over those players though is that he's reaching his peak, whereas they were on their way down.
I suppose I'll say, Madine is more likely to be a steady, decent player, but Diony is more likely to be good enough for the Premiership (and also more likely to be a total flop).
