My M700 has been fairly hit and miss since I installed it last November. I would say my garden is decently challenging given the shape and 'terrain' (not to mention fallen branches, leaves and children's toys), but I didn't expect as much difficulty as I've had.
It mostly comes down to three things.
First I need to be more clever about how the wire is set up. Sadly, I need to be more forgiving around corners and obstacles, as he just gets in a tizz all too often navigating around things.
Secondly, his traction is not what I'd hoped for. Any part of the garden that isn't nice easy turf is subject to getting ripped up by the wheels, often requiring a rescue and tidy up job.
Thirdly, I do have a lot of immovable obstacles (i.e. raised beds), and he just doesn't get as much of a clear path, or nice open space, as he'd like.
I haven't given up hope yet, just need to buy some more cables and connectors and find a spare 3 hours to sort it out.
Almost forgot to mention, he managed to cut his own wire the other day. You'd think that wouldn't be possible, but there we are. I really did do a proper job of nailing them all down when I first did it, but I imagine over time he might have indirectly dug it up himself, then somehow got tangled with it.