Fullrange-
There are less than a handful of fretless Dingwalls circulating, so the liklihood of bumping into one is small (unless you live in Houston TX-which appear to have 2). I'm not aware that Sheldon has made a higher end model in fretless, but hes made a few ABIs, ABII, and SuperJs in fretless.
Funksway and I both have fretless AB basses.
As you suggest a Dingwall fretless is nothing but a great Dingwall bass w/ Mwah, all the evenness of tone, string-to-string tension consistancy, punch, playability is all there. Only thing missing are frets.
Sheldons magical mix of epoxy coated fingerboards add a bit more sparkle than maybe your used to hearing onhis basses, but overall its really a Dingwall bass.
If you are a competent fretless player, and your comfortable on the fretless- you wil have NO issue playing a Novax fretless.
I've had my ABIfretless since 03, and I feel very comfortable on it-tone and intonation-wise-if I ever considered another Dingwall fretless i would order it unlined, it really is no different a beast.
If you have any specific questions or concerns- besides how do i play it I'll gladly answer
Hopefully Funksway(Peyson) will jump in