I can say with honesty that I can't tell the difference between these MRE heaters and the real deal. From that unmistakable green to the horrible stench they create these things are true to form.
I used them at work, in the cold, time and time again and they got my food hot. I'll have to point out that they take a few minutes so don't think of them as a microwave on the go.
Still these get the job done if you're camping, in an emergency, or just working at some crap hole at night without power.