Mixed Member Proportional elections, called Additional Member System, in the UK, is a doubly safe seat system of dual candidature (blithely endorsed by the Canadian lawyers commission) which the Richard Commission, on the Welsh Assembly, denounced because it denies the fundamental democratic right to reject candidates. The report recommended its replacement by the Single Transferable Vote. STV was recommended by the BC Citizens Assembly, which was an independent referee, unlike that anthology of political contestants, who cannot be their own referees. 
Richard Lung. "Democracy Science" links 3 free election method e-books.