Well I am a Harmony 659 user. I use to have a pronto and hated the lcd touchscreen. IMHO touchscreens are the worst UI for a remote control.
That said I really like the 659, super easy to program, and super easy for anyone to use. My wife loves the 659, she has yet to have any issue using it. Guests have come over and have no issue using it either.
One thing I really like about the 659 that many remotes do not have including the pronto is state tracking. It remembers the last state of a device, this is very useful for things that do not have discrete codes like my TV. So if I am watching TV and want to listen to a CD it knows to turn the TV off and switch the input of the reciever to CD, but if I am watching TV and switch to watch a DVD it knows NOT to send the on/off signal to the TV.
It also has a "Help" button that is very useful for when things get out of state. Which happens if the IR signal is blocked for some reason. Big yellow button says help and it walks you through a few yes/no questions to get you back to a known state, very wife friendly.
Bad points - The LCD is small and it looks to have room for 6 functions, but alot of the time it only allows for 4 at a time.
- The transport buttons are on the very bottom of the remote, can be diffcult to use for some. I have gotten use to it, and I use them alot for Tivo
- No user defineable macros, some have "taught" macros to it. This is not much of an issue for me since I can get all the macro functions I need through the Activites options. You can tell it to do certain additional things when starting or ending an activity.
-The default remote database is sometimes a little off, can be fixed by learning the codes yourself
Possible bad/or good
- All setup is through the web interface so if you like it great, if you don't then not good. You can setup your remote before buying the remote, I recommend you do that.
Other Good Points
- Nice size, not too big.
- Very nice button feedback
- Setup super simple
- Easy to use, plenty of buttons
I did not compare with the MX-500 cause I have never used one.