just changed my rounds on my fretless squier vmJ to rotosound flats - bit more tensions and tweak the truss but tone is ok ...
BUT ...
once you bought and used a set of la bella's, frankly you'd be rather daft to want to play anything else for tone and tension - ok so im daft but in my defence the rotosound flats were just an experiment and to support homegrown manufacturers but in future id rather wait/save up and get the LB's than buy a cheap set