I've got some cheap one which under the plastic is the same as the flymo and the husqavarna (all the hacks etc. for them work on mine - eg. expert mode - which is a great way to find breaks - never had luck with the various other suggestions radios/etc)
I really like it - over summer I had guid-wire problems and was manually mowing my back garden, and whilst I liked getting out and about, it was a pain in the arse (especially if I let it lapse and had to wade through longer grass)
Mine does a great job of the front garden, but isn't very good at following the line out as it should to do the back because of a narrow corridor + trampoline legs in the way. Which is a software thing, and I can't get it upgraded, but it's not enough to upset me - it does make it into the back, and I just pick it up and take it there sometimes (it makes its own way home to charge)
If you have lots of lumps and bumps it's going to be a pain - mine likes to throw itself off the side of my garden in winter, and gets stranded on sticks if I don't go and clear them from the garden (large ash trees). You will have little grass fringes everywhere you have an edge.
I would also say that keep it simple when laying the guidewire. Unless you have professionals with a machine, don't bury it, and don't bother carefully laying it round obstacles that can cope with being bumped into. Leave a few spare loops at corners so you have slack if you need to repair/diagnose breaks, and get a big bag of the gel-filled 3M connectors, and a spare reel of wire.
I laid my first guidewire 2 years ago. This summer I laid a new one following weeks of mucking about trying to find a break, plus I'd learned some lessons from the first time.