I occasionally used the standard 510 sound bar previously, but purchased the 511 to match my new Dell 2713HM monitor as I now needed a black one.
Overall I think the 511 does sound a little better, and is certainly better finished a looks a lot better when fitted to the monitor.
Sound quality is very clear, though as one would expect the low bass sound are a little limited, switching on the bass enhancement does help however and I find the sound quite acceptable.
All the controls are touch sensitive buttons and seem to work well, my main moan is the fact although the unit remembers all the settings when put into standby, it does not retain any settings when it's completely powered off at the mains, which is a bit of a nuisance, though it only takes couple of seconds to power on and adjust the settings again.
Also because this unit draws more power than the standard 510 it uses a separate power supply, so unlike the 510 which only needs 1amp this unit has a separate power supply rated at 2amps which is probably a bit too much for the monitor to supply, so cannot be powered from the monitor.
Is it worth paying the extra money for this unit over the standard 510, well that is debatable, it certainly looks a lot better when fitted to the monitor, and as stated it sounds a little better, so I think the answer has to be a yes. However.. value for money wise with simple on-off volume control and still with acceptable sound + the benefit of drawing it's power from the actual monitor the 510 will also do the job at a much lower price, this 511 just looks much better so no regrets buying it.