Well, not an OlliOlli expert, but played it on PS4 and Vita back then, so...some quick notes:
-Game is on sale until March 19 for $8.49 (in NA at least).
-Unlike Mario vs DK on which you get a code in the receipt for the other version that you can share/gift/sell; cross buy is like other platforms. You buy one version, the other is marked as free so you "buy" the free version to have the other one. So, both units need to share the same NNID of course.
-Wii U version looks like (how I remember) the PS4 version. Clean, colorful. No noticeable problems. Gamepad displays buttons, etc. and a quick reset option.
-Game looks decent on 3DS, though others has said is not 3D. I'm playing on a 2DS anyway. It is literally the same game but at low-res.
Overall, anyone that was aware of this game and hasn't tried it, less than $9 you get 2 versions of a great game.