i’ve been using a 305 for a few years now and wouldnt be without it now. plan your route in memorymap before you set off ensuring your waypoints are arranged in such a way that each turn sets you off in the right direction and every junction has a waypoint even if its straight ahead. you quickly learn how to create good quality routes.
lack of maps means its not a lot of use getting you back on track once your lost, and lack of OS grid means using LatLong to find position on a map, but in any case it’ll show you the direction of your closest waypoint.
from what ive seen of the 705, the detail of the maps look like they’d be little use off-road anyway
understand how to use it and appreciate it’s limitations and you’ll get on fine – especially at the price they go for these days!