I must admit that I was originally a little disappointed with my Zodiac T3 robot which we bought back in 2013; it didn't seem to reach all corners, or cover the whole bottom surface, and was regularly getting tangled.
Our pool is 9 by 4 metres, and I use 7 interlocking sections of tubing between the business end, and the vacuum outlet.
This Spring, I noticed that the rubber seal which fits between the pipe and the vacuum outlet hole (the blue multi ribbed affair above) had 'perished', and was falling apart, so I decided that, rather than buy an expensive new piece, I would make my own version by elongating the whole lot by adding an extra foot or so of ordinary spare vacuum pipe, and glueing onto it a cheap white plastic connector (see top photo).
I don't know quite what this extra flexibility has done to the robot, but it now cleans the bottom almost perfectly, and no longer gets tangled. In fact it's so much better that I did consider offering my simple invention to Zodiac; 'gratis'.