As pcaouolte says, they will do large areas and go back to base to re-charge when they get low but you do have to be careful siting the return wire. It needs to be quite central through the lawn as it goes searching for it to find it's way home. It will normally run slightly to the left of the wire when returning home so make sure you site it as advised in the booklet.
The boundary wire can be set into the soil rather than be pegged on top. This prevents any potential snags if the ground undulates or the pegs become loose if the ground dries out in hot weather. It's advisable to peg it out when first setting up so you can adjust how close/far from any flower beds or drop off points. Once you are happy with the set up it's simply a matter of using an edging spade to form a slit, drop the cable into it and press the soil back over the slit to hide the wire. I think you can bury it up to about 200mm but 20-25 is deep enough. The grass will grow back over the slit you made so it becomes invisible. They have sensors to stop them going too far over the boundary wire and if the bump into an obstacle they will simply reverse and go in another direction. They are quite weatherproof but do need to be put in a dry place over winter, preferably in somewhere that doesn't drop below about 4 degrees C to protect the battery. As stated, they cut clippings and drop them back on the lawn as a form of fertilizer. The blade height can be adjusted to cut more or less, depending on how quick it grows. You can programme the days and times when you want it to cut and they are usually pin coded which you need to input to programme or make changes to the settings. It also stops it being used on another base if it is stolen. New blades are fairly cheap and last quite a while. I think on average I change ours at the beginning and then mid way through the season. You can get 9 blades, (they usually take 3), and 9 screws for around a tenner. Always use new screws with new blades. Extra cable is quite cheap if you need it but the 100 metres you get with it is usually sufficient.
We have a Flymo 300R, (about 3 years old now and still in fine fettle), but I think you can get them with Bluetooth or wireless remote these days. Our main lawn is about 18metres by 15metres and it copes quite well with it. It will even get up an area which has an incline of about 20-25 degrees if the grass is dry. I would recommend one but Google the instructions of the one you decide on to see how difficult/easy it may be to do in your particular situation. You may spend a fair bit of time on your knees installing the cables but once done you can set it up and leave it to get on with it while you relax.