The Double D is a dual delay with one standard and one optimised for shorter, brighter slap-back delays.
The Dawn Chorus is a modified clone of the Boss CE2. It features a stereo output and has switchable intensity modes and a chorus/vibrato switch, to take you into the fast Leslie realm.
An extra feature is a separate supply rail for the LFO so there's no chance of any errant popping or ticking, which the original was prone to.