As an MC15 Super mkII owner I'd say this :
The MC15 is better value but the MC25FL is better built.
I wouldn't consider paying the price difference for my
tuned SystemDek IIX / Rega RB250 combination.
Compared to other silly priced MC's the MC25FL looks
good value for for its build and tip quality, but what we
are really talking about is hitting price points for what
can only be called gullible consumers.
I wouldn't expect the the MC25FL to be much better than
the MC15 in an RPM6, IMO paying the premium for the
MC25FL would require a seriously tuned top notch set-up.