If your talking about signings from English lower leagues then I would argue that he has not had an 80% success rate
osman and Edwards yes
buaben and Taylor were excellent (but you could argue they would have been well known for what he did at Scottish teams like Dundee United, Falkirk etc
amoo was okay
dumbaya and seaborne were perma crocks and cannot be said to be successes in my book in fact giving how much they actually played
but I cannot agree that guys like Richards Everton, keown, mukendi, carroll, German, Cargil, turnbull, Banton, moncur, eccleston, pogba And azeez were in any way successful at all and possibly not very cheap either