Got Doop Freestyle 2015 recently. They are great and have adjustable shoe size and there is a small discomfort because of it.
The problem is that with adjustable heel fitted on (it could be replaced with a screw) your heel is 1cm higher than your toes, which makes your feet very uncomfortable in the middle.
The solution was to use double sided tape and stick half of the slippers. It's great as it also gives your extra foam suspension.