The real power for me came from the buttons being reassignable for each activity. If you have 'Watch TV' where it only uses the tv, then the volume buttons work the tv volume. If you have another activity called 'TV through Stereo' or something then the volume buttons can be assigned to the receiver/stereo etc. This means everything can be intuitive and just work how people expect it to. None of that I have to select the stereo device to work the volume and then back to the tv device to change channels that basic universal remotes require.
There are a few provisos though to ensure it all works well. Some will be easy, others annoyingly hard.
a) everything HAS to be in standby off prior to using any activity. This is the only way the remote knows everything is in the right on/off state to start with.
b) if you want to control something that's not ir (or rf on some older models) you need some form of ir to bluetooth etc type adaptor. Harmony do one for the PS3 so if you want to use this with a ps3 buy that one specifically to save the heartache.
c) you have to keep it pointed in the gear direction for the whole startup/shut down sequence, very important, especially for ps3 use.
d) your gear should have discrete input commands to avoid the need for crap sequences etc so you know what input it's looking at.
Apart from that, any harmony remote basically works the same, they just get more additional features as you go up the scale, and build quality really. they have movement sensors that illuminate the buttons, very cool. You have to have an internet connection too, something to consider possibly.