You'll struggle to get an output of more than 100W/m2 to be honest, and even that would need you to screed over your pipework to create a more even distribution.
You also need a manifold as underfloor heating works at much cooler temperatures to a traditional radiator system (you don't want water circulating at 80-ish degrees where your bare tootsies are likely to touch) therefore a temperature mixing manifold is required to cool the primary flow temperature to your underfloor pipework.
The other thing to consider is how well insulated your room is. In my (entirely commercial) experience u/floor is only used on its own in new builds with extremely well insulated rooms. In existing installations, you'd only use it to take the chill off a wood or tiled floor.
You also need a manifold as underfloor heating works at much cooler temperatures to a traditional radiator system (you don't want water circulating at 80-ish degrees where your bare tootsies are likely to touch) therefore a temperature mixing manifold is required to cool the primary flow temperature to your underfloor pipework.
The other thing to consider is how well insulated your room is. In my (entirely commercial) experience u/floor is only used on its own in new builds with extremely well insulated rooms. In existing installations, you'd only use it to take the chill off a wood or tiled floor.