To see topo maps must use Basecamp,if GPSmap 421 dont lists 'Garmin TOPO Sweden Friluftskartan Pro v2 - Norra Norrland' as compatible, it wont show it with all its features.
I can see the GPSMAP 620 and GPSMAP 640 in the map compatibility list or some nuvis, like series 22xx , 12xx,14xx, 37xx, 500 and obviously outdoor gps units