TOPO U.S. 24K vs Garmin Montana 700i built in topo map

The built-in Topo Active maps are based on OSM. I do not know the scale. They seem to have less detail than the USGS 7.5 minute quads (1:24000). OTOH, OSM tends to do better than (some) other cartography with regard to streets and trails.

In general, coverage of trails is spotty on any map you purchase. In my experience, you are better off with crowd-sourced tracks for trails in the area you plan to visit (for example, AllTrails).

Since the TopoActive maps are included with 7x0i, best bet would be to check them out before spending money on more maps.