Disclaimer: Yes, I eat them, No, I don't like them.
They have a place. They were designed to be used in a fairly short time after manufacture.
They are NOT (imo) intended for long term "prepper" supplies.
If you want them, they are best if rotated (eaten and replaced regularly).
I will have a few (one or two ) in my BOB or INCH bag, but no more than that.
This article lists specific reasons for NOT using MREs,
Please read it and make your own decision.
http://preparednessadvice.com/food_storage/twelve-reasons-store-mres/