I think that Blackwood (in any flavour) is the most misused and abused convention in Bridge to the extent that when opponents use it, 70% of the time I sit back and wait for my good result.
I like to play that once both hands have made a cue bid Blackwood becomes redundant and a bid of 4NT is a trump cue, showing Ace or King of trumps and requests further cue bids from partner. This means that ExRKCB only applies when you jump to the 5 level.