We’ve got 20 x 50W downlighters in our kitchen (it’s a big kitchen), divided into 3 dimmable zones. The main issues I’ve had (besides effectively running at, I assume, levels of energy consumption matching our microwave when they’re all burning at full 1000W) are that the bulbs don’t seem to last long and the 3 switch dimmer control unit blows a lot. I replace a bulb at least once a week and I gather that there are issues if you try to control them with a dimmer (in that the switches often blow). There is a floor above our kitchen, so no lagging directly above the bulbs and I would assume that any heat inefficiencies given off by the bulbs would be offset by reduced output from trv controlled rads?
They work well and Mrs T likes them, but I doubt that they’re cheap to run or very ecological. Still, looking on the bright (!) side, there’s not a lot of chance of getting seasonal affective disorder when they’re all switched on at breakfast……