You can't go wrong with either. They're almost identical. The finish is slightly different. The R91 needs an adapter (which is included) to use a different tip. The location of the air adjustment screw is different (but functionally the same). They're both about equally difficult to get & both are selling out just as quickly. If you find you have a slight preference of one over the other, wait it out & get that one. Otherwise get whichever is available. The preference between the 2 is going to be personal instead of universal... neither is really 'better'. (And yes, the R91, technically is a clone, but don't confuse clone with 'cheap chinese knock-off'... for once it isn't)
This is all provided you are looking at both authentic models.
I completely recant my statement. I just received my authentic R91 today. It is not as good as the KFL+ in function. Besides the machining being extremely poor, the juice channels are not cut properly which will affect it's function drastically. I'm returning it & buying another authentic KFL+.