Just boiling the pouch in the water shouldn't affect the water (unless the pouch is dirty). I know the chemicals in the flameless heater are supposed to make the water undrinkable, but since the amount of water is so small its not really an issue.

+1 on field striping makes MREs much smaller and you can discard things you don't like or need. Over several days, the lack of extra protective packaging won't really be missed.

US MREs also come with a "hot beverage bag" which is a thick ziplock bag. Useful for all kinds of things, not just making hot chocolate, tea or coffee. Carrying the hot beverage bag, flameless heater and beverage powder of your choice is a light easy way to have a hot drink on a short hike when you don't want to carry a lot of gear. Very useful.

Looks like the IMP has both pluses and minuses compared to the MRE. I'd be interested in doing a side by side taste comparison.