Well, with "all friends and close family" clause this will probably have cascading effects...

It looks like even people who consider MWI the best model would still prefer to survive in all the branches where it is possible and more or less comfortable.

If someone creates such device, it will probably be set to truly crippling damage as threshold and will lack synchronisation. This way it will gain its market - but the users won't consider the branch where they survive as relevant... QI stories will be used simply to paint accusations of assisting suicide as religious intolerance.