We had a built in GE oven for 203 years and were happy with it.  This one fit exactly into the opening so we bought it.  BTW, the old one was still working, it just got a bit dirty over time.  The new unit is great with 2 exceptions.  The lower wattage causes it to take 50-75% longer to bring it up to temperature.  The second is the microwave oven human interface.  I found the old one much easier to use for short, simple zaps.