I've tried using the MM for inspections in my own factory. Few things to note:
1) When you are indoors with no GPS, the MM refused to fly higher than 10-15 ft. You can trick it by placing a table/scaffold beneath it.
2) When flying over pipes and ductings, downwards sensors will make your MM raise up, need to watch out on that.
3) If you's flying into a duct where only MM will fit in, DON'T. If you crash, extraction will be difficult. You may lose signal as well.
I'd advice getting a wired RC vehicle with camera for those due to signal issues.
Just my 2 cents worth.