We are extending the house with a new living area and a bathroom. We expect the concrete slab will be done in by end-May.
At this stage we are thinking of Under-tile heating, but if your advice was In-screed, we shall have to decide reasonably soon.
We are also planning to add under-floor heating to an existing bathroom which is being changed into an en-suite. I expect this will have to be Under-tile.
Please see Page 2 of the plan to get a sense of the area under consideration.