Mixing the two technologies (motor & Unicable) over multiple boxes is indeed a bad idea, as explained here.
But there is a use-case for mixing them for multiple tuners in one receiver. That's because in this case E2 'knows' which satellite the dish is pointing to, and takes this into account when creating timers.
A motorised dish with a (dual) Unicable can feed two tuners, thus allowing you to see/record simultaneously from e.g. BBC1 & 2 & 4.