The Boss DD-500 is one hell of a unit! I have it on rental for one month at L&M, and then I will be buying it outright. The rental is just to get set up/make sure it does the trick, and have time to move my Flashback X4.
I wanted the opportunities to keep up with my bandmates DL4's wild side, and the DD-500 makes a pretty good go of it! I had read the manual and a 39-page TGP thread already so I knew some of the deep editing options before I even laid eyes on it. I still found it very intuitive and easy to get up and running. I'm using it with the Artist V into a Marshall MG15, soon to be into garage band instead.
The main seller for me is the parameters you can control without needing your computer. The Tap/CTL feature is very handy - you can set it up for some cool stuff. With this pedal, you're able to limit the number of banks you want to use. That was great for me to learn, as I had trouble with the Empress VMSD regarding overwriting and changing presets. The Flashback requires you to hold the button to save a preset, whereas this requires you to use the exit/edit buttons simultaneously. This means I can't accidentally change my space echo to 2290 in the middle of a gig (which I have done). It is very easy to bank up and down, and there is a system setting for banking wherein the unit will wait until a switch is pressed to change banks, or change automatically.
Having the Tera Echo and SFX options open up some weirdness for live use, which I look forward to dialling in. I think our producer is going to have a blast with this when I get in the studio next month.