fgc,
I can't compare the Digital to the Ultra, as I only have the Digital, but heres what I can tell you about the Digital in general:
Digital has six reticles, none with a circle, vs. Ultra's 5;
When mounted on the flat-top receiver, Digital sits high enough that front sight is in the lower 20-25% of the lens (only the crown formed by the ears and front sight post, and maybe 1/4 inch below that are visible in the lens);
Co-witness is possible, but not absolute/same plane co-witness (see above);
When mounted solely over the receiver (slots T7 and T13), the rear of the Digital hangs over the rear of slot T1 by about 3/16ths inch. I don't think a BUIS can be used with the Digital mounted solely over the receiver;
Return-to-zero in both windage and elevation is by springs. Whereas the elevation r-t-z on mine is positive, the windage r-t-z is a little mushy. That could just be mine though.
I've not shot 3 gun, but for plinking it seems to be plenty adequate. I've not yet shot mine while mounted on the flat-top, nor at distances past 100 yards, but for plinking when mounted on a handguard rail it seemed perfectly adequate. I just wish they could desing a lower profile, more positive base for it.
HTH,
Rich