I've got 2 garmin devices, one for running, one for cycling. However for map displays when out walking I use the
SATMAP 10.
Great features, great battery life (10hrs) - the downside is you need to buy SD cards with maps on them - broken up into regions at varying costs. You can use generic programmes such as
www.mapometer.com etc to draw up routes before hand and drop them into the device. They will then display as an overlay on the map.
It will display 1:25,000 OS Maps (explorer series) or maps of lesser scale if you wish.
Worth a look on their own website satmap.com but available cheaper on the web