If done smartly, they can be a good option. And, depending on your style, they can be lighter, despite the water carried.

I should probably qualify that. First, you should take them apart and only take what you need. Second, don't take a stove or fuel. Only heat your meals with the heater. This means no hot drinks, unless you use something other than a stove to heat it. If you do this for only a few nights, then it is lighter than dehydrated food with a stove and fuel. However, there is a point in time that dehydrated food with stove and fuel get lighter.

So basically, MRE's have their place. You just have to figure out if it is with you.