my take on this whole nano-in-a-cube is this:
i've kept roses in a 12 gallon, a 24 gallon, and a 28 gallon--those AIO nanocubes and they did seemingly ok, seemed "happy" enough, and i was one who scoffed at the people who said "it shouldn't be done in a nano".
in fact, the 28 was an exclusive BTA-only tank, so I wasn't even worrying about them wandering/stinging/chemical warfare, etc.
but in the end, when I upgraded to my 56 gallon current tank, that was when i found out just how much happier they could be in a larger tank: they FULLY expanded, grew SO much faster! SPLIT more often! probably due to: better, more STABLE water quality, better lighting (hopefully nobody's putting their BTA under stock nanocube PC lighting here), and more room for them to move around to find their "happy spot", more rockwork and more options to find their favorite spot (as opposed to a more limited amount of rockwork/space in a nanocube)
so, yes, if you want to, it CAN be done (comparing their happiness to a dog's happiness living in a small place is a whole 'nother issue that i don't even want to get into), but to get a TRULY happy rose that's THRIVING, i'd definitely go larger on the tank ... and would i ever put a BTA in a nano again? NEVER AGAIN

(i still have my nanocubes up and running right now! lol)
just my 2 cents ...