Ah didn't realise the dimensions were quite that small! That does mean that this takes up 2/3rds of the cubesat, which sounds like it would be impractical for many purposes.
This one flew on a 6U (~35x20x10) and that's really the minimum size for this kind of engines. And even on a 6U, the power limitations make us think twice before putting an engine, it really has to be needed.
