Approval voting has the same problem as any other scheme which doesn't force an exhaustive enumeration of preferences: political parties can and will turn them

Approval voting has the same problem as any other scheme which doesn't force an exhaustive enumeration of preferences: political parties can and will turn them into de facto first-past-the-post systems. How? "Just vote one". Or "just mark one". Or "100 points for us and 0 for anyone else". Etc etc. Enough voters will comply -- especially in voluntary systems which magnify the power of fringe voters -- that any advantages of non-ranking voting schemes will be neutralised. Voting systems like approval voting, range voting and so on work if the options or candidates are prepared to behave uprightly. Outside of situations like a local club or professional organisation, they won't. They will meta-game. It happened in Queensland when they introduced "optional preferential" voting.