Having had my Nalu for a couple of weeks now I would have to say it definitely is a better all round board than the Mana from my point of view.
It paddles better.
Catches waves way easier.
For my money it surfs better, but you have to walk it long board style to get the most out the board.
You have to turn it off the tail on bottom turns or it takes for ever to drag it around.
It is not as stable as the Mana - I noticed yesterday when paddling past some cliffs the rebound from the waves meeting the swell was more challenging than on the Mana.
It is more responsive than the Mana on a wave - it's hard to believe a board 11' long actually surfs well.
It does have quite a bit of nose and tail rocker so it is not the fastest flat water paddler but significantly faster than the Mana with better tracking.
In saying all this I still think that the Mana GT 10' is a good board for a bigger paddler looking for an all round board to get into SUP. The Nalu is going to be my 1 board quiver for a while - although I sometimes like the idea of a dedicated flat water/ocean exploring board as well
BTW where do the board companies get the maximum rider weights for their boards from? Apparently I am 10kgs too heavy for the Nalu!