For those not familiar, 50% cooking power on a conventional microwave is 100% half the time. 50% on an inverter microwave is 50% power all the time. I really wish I knew if it made a difference in the actual cooking. What I do know is this: Inverter is really good for RVing since a lower setting reduces the actual power input requirement. This could allow for use on a portable generator, or keep from popping circuit breakers when CG pedestal power is running short.
But Inverter is more expensive and seems to be less reliable. Daughter had a residential over-stove/under-cabinet with fan etc. Kenmore Elite or some name like that, actually an LG. When it quit, we looked on the web and found most of those did and the repairs weren't economic. Either that or the part was discontinued, I forget which. So, if a smaller, less powerful microwave will do what you want, it'll cost less and maybe last longer. Just match up dimensions and move the mounting brackets to the replacement unit. On a job like this, I suggest making a drill stop so the bit just passes through the outer shell without risk of punching into the inside of the unit.