Regarding your question about the tone curve, you can work with tone curves but not the custom point RGB curve, only the Region curve (Parametric curve) using 4 knobs to control regions and 3 to control divisions, I use it like that, is not as precise as the point curve but it's quite powerful, so when developing I use parametric curve to deal with the first part and then if I need some more precision I go to the custom RGB curves and deal with them manually. At first I thought it was quite inconvenient not to be able to use knobs for the tone curve (point RGB curve) but then I used it like this and I've overcome that issue, it's a question of adaptability.
I have had the X-touch mini for a year and a half now and find it very useful, I haven't use the p-fixer but have seen Int and I truly believe the x-touch with the midi2lr is quite better. The p-fixer is just an x-touch labeled for their software. In Midi2lr I created my own layout with 8 profiles and designed the labels for it, had it printed on some sticker paper and placed it over the x-touch and it looks great, I honestly don't look at the labels any more since I've memorized the layout.
Hope this addresses your questions.