New GPSMAP handheld models and TopoActive mapping

Sorry if this is not seen as a BaseCamp Mac question, but a big part of my use of BaseCamp is connecting my handheld and using the maps installed on it while working with waypoints and tracks, etc.

I've been comparing the new 66sr to my existing 64st (and my original replacement idea, which is still available, the 66st). In their specs pages, I found what seemed like a major change in maps preloaded on the models which were most recently introduced: TopoActive mapping vs the more familiar 100K US+Canada topographic maps. What are the differences? And, are there new concerns with the manner in which handhelds with this newer map technology display in BaseCamp?

And, an aside: "Multi-band technology" is also advertised on these new models... is this a big improvement over the antenna on the 64st and 66st?