I don't see foam core as being any better or worse then built up. Some people find it easier, some don't. Quicker?? Sometimes but I build fast enough that it takes me about the same time to frame up as it does to sheet a core. The guys that build a lot of foam core planes use a vacuum bag system to suck down the sheeting, I use a couple hundred pounds of lead shot bags. I just haven't had enough foam core kits to go to the trouble of the vacuum bag. I do now have a foam cutter now so maybe in the future?