Where the compromises exist are the lack of onboard scheduling (available only on the 600 series flagship the iRobot Roomba 650) meaning you will have to start it manually each time while virtual wall 'lighthouses' (markers which stop the Roomba from crossing an invisible line) have to be bought separately.
iRobot Roomba 620 Performance
So how does all this come together? The answer is rather well, though there are limitations. What is immediately clear is that the iRobot Roomba 620 is a significant improvement of the ageing 500 series it supersedes. Initial mapping of a room can be slow and a little haphazard, but the iRobot Roomba 620 learns quickly and is eager to dig into every nook and cranny it can find before making long, sweeping passes on wide open areas of floor. iRobot doesn't specifically mention battery life, but we also found this to be much better with the 620, lasting roughly 80 minutes on a single charge – almost as long as the 50 per cent increase championed in the 780 which saw it last 90 minutes.
As well as navigation and stamina, cleaning performance has also taken a leap putting it almost on par with its more pricey stable mates. Robot vacuums still won't pick up as much dirt as a manual vacuum, but the iRobot Roomba 620 does a fine job of picking up debris roughly to the size of popcorn and is effective at collecting fluff and dust – the latter of which has historically been spread around as much as picked up on hard floors.
Where are the negatives? The most obvious point is one inherent to all Roombas: they remain 'bump bots'. This somewhat derogatory term has come to categorise robot vacuums which regularly make contact with their environment as they work out a room. They also appear less logical with their multiple pass system which can appear fairly random to the naked eye. They are best left on their own since the end results are excellent, rather than watched.
The upside is this bumping approach tends to be more impetuous with tenacity for digging into hard to reach areas; the downside is they slightly jog the environment around them – most notably if they get behind open doors whereupon they push them shut locking themselves in rooms. This requires a certain amount of 'Roomba proofing' before starting a clean. The flipside to this approach is the somewhat misleading 'SLAM' (Simultaneous Localization and Mapping) technology seen in Neato's products, including the Neato XV-25 and Neato XV-11. They tend to trace the outline of a room before neatly vacuuming the middle and they barely touch anything. Against this they can skip over tight areas the Roombas belligerently attack. The choice is yours.