The Track kit is a very easy build, more like assembly than building, and parts are of very good quality and, as you mentioned, there are several options in barrels, even rifled barrels. The Sitting Fox kits have an attractive price and probably make up a decent gun but I've never actually handled one. All of the modern trade gun replicas make a heavy gun because barrel walls are much thicker than the originals which were ground to very thin barrel walls. Also the modern replicas use the same exterior barrel profile regardless of bore size so the smaller bores, 28 and 24 gage are even heavier than the 20 gage.