1) These peaks are significant (at least in the U.S.), in terms of the size of the peak, but the duration isn't all that long (assuming that these things are used as the peakiest of the peakers). And I presume they have a mode that sheds the heat outside- this loses the CHP part of the equation, but this should be a small part of the work cycle (these things should run most of the winter and a few 10's of hours in the summer). You could even do trigeneration (where you generate electricity plus cooling), but I suspect the thermodynamics won't work for these units.
2) It's burning natural gas, so it's easy to be clean. The cost-competitive part comes from CHP: traditional electricity generation wastes 2/3 of the input energy as "waste" heat; these don't (as long as they put in 80+% of their hours during heating season).
I have a system in my basement that's 1/2 way to CHP now (it's an integrated engine plus boiler; I just have the boiler part so far). See Freewatt. The pure economics of adding the generator are kind of blah, but it is more energy efficient, and that has value to me.