My first GE Profile OTR microwave used two 20W halogen bulbs, but is near the back of the unit, so didn't illuminate the stove-top well. After 7 year when the magnetron went out, I replaced it with a GE Profile OTR Convection/Microwave unit, since I wanted the added convection feature. This unit has one 50W halogen bulb, but is closer to the front, so it illuminates the range a top better. I have yet to see any brand use LEDs for lighting, mostly because they have to withstand heat coming from the range below it.

OTR MWs offer suboptimal venting, lighting, and (unless you are very tall) MW ergonomics.

I don't think the space savings are a fair trade-off even in a tiny kitchen.