I found the over the head ones were okay to put on but very difficult to take off to the point Jake near on got strangled. I exchanged it for a step in harness which I find fantastic.
However the difference in sizes is huge. I have a medium for Jake and it is a little big but we can get away with it. For Red the medium is hugely massive on him but the small is a bit tight so can't use it. The difference between small and meduim is quite big and I wished that it wasn't so as I love them. Now I have no idea which harness to get for Red as I like the step in ones.