I'm interested in this comparison as well. I love the reverse effect. My favorite band The Cure uses it all over their Bloodflowers album.
have you tried doing volume swells with a simple volume pedal? its a similar thing
No but I just received A FV-50L in the mail yesterday so...
I own a DD-6 and it pretty much is always on reverse mode. If you listen to the Bloodflowers song Watching Me Fall it is a very prevalent effect. I do believe that two DD pedals are used at once weather they are both DD-5s or DD-6s or both in reverse mode I can't tell, but I'm sure there are two DDs used.
Anyway I'd love to get my hands on a second DD-6 and see what a double reverse digital delay can sound like.