We purchased our Thule Chariot in part because of compatibility with the cross-country ski kit and we could not be more pleased with the investment.
Swap out process between strolling/ski mode is fairly straight forward and becomes easy enough with practice. Strongly recommend practicing a few times indoors before doing it in the cold while juggling babies. The waist belt is comfortable, I was able to pull child #1 while pregnant with child #2, until well into the 3rd trimester.
Pulling a full double chariot does take more effort than skiing solo, but we have found it incredibly useful for our family. Whether I am taking both children out alone, or both parents are switching off on weekend adventures, it has allowed our family to stay active all winter long.
Absolute favourite piece of parenting gear we have. Well worth the investment.