We’ve had two OTR microwaves. One came with the house, and the other was a replacement when the first one died. I had no idea how much work it would be to install the replacement. I guess I kind of assumed it’d be a ‘plug-and-play’ situation, but far from it. Even though the replacement was the same brand as the first one, the mounting bracket didn’t align, nor did the vent/chimney assembly, so the installer basically had to do some patching from the first one and install the second one afresh.
After about 15 years, the replacement failed. It is now a storage cubby, and we are currently using a countertop MW. Eventually, we plan to remodel the kitchen and install a proper vent hood where the defunct MW is now. The built-in fan never did that great a job venting anyway.