using a 10 gal as a growout tank vs. a permanent home are entirely different things. that's also not to mention that all of the "plug-n-play" tanx run a good 6* or more too hot for even tropical species SH, and they also typically need to be repumped, partially to help resolve heat issues as well as to bring the flow in line, altho you can split the flow and that will work as well.
also, the "12 gal" nanocube only holds about 8 gals and change (i own one), so you're already well behind the eight ball in terms of water volume.