Transferring the save data between 3DS and Wii U is really quick. There is an application that you need to download on the 3DS, but after that, you just follow the on screen prompts on the Wii U and 3DS, and you're good to go. It just took a few seconds. Less than 30, if I remember correctly (I did this back in December).
I think the addition of Off-Play is a good thing and something that tons of people and the West seemed to have been clamoring for with this game. For the Japanese, I honestly have no idea. At any rates, it beats the previous Off-TV solution of NEEDING a 3DS and a copy of the game on top of the Wii U version. :-|