I have to cast my vote along with Arjen. I too ended up swapping my RTI for the MX-500 because there were not enough hard buttons. Transport controls would have made that switch unthinkable.

My RTI fell off the end table last night and I did not bother to go pick it up. That was the tell tale sign that it has been replaced. I like almost everything about the RTI better than the MX-500, but the lack of hard buttons is enough to sway me.

I am not 100% sure that simply adding a transport control would be enough to convince me to upgrade again. The Price to Performance ratio on the MX-500 is a powerful draw. I much prefer the RTI's power and even the feel of the buttons, but the MX-500 gets the job done quite well. The more I get used to it the harder it would be to justify another upgrade. :)