I’ve also been using both lately and I agree with everything said here.The Flexi is kinda the better Rex. Athleast IMHO.
I have both and the rex has noticeable more blade exposure and at least I have to dial the rex about 0.5-1 number down compared to the Flexi.
Using the Rex you have to pay more attention and the steel gives a liitle drag quite easily.
On the other hand the flexi is much heavier but smoother on any setting.
I use the flexi on 2-2,5, the rex on 1,3-1,6.
So I'd recommend the Rex to advanced shavers with a liking for blade feel and stainless steel. The flexi is almost as easy to use as the Rockwell.
And remind it comes with a very useful stand.
But in the end they shave very similar I must admit.