My initial observations are they're highly complimentary of each other.

DMM: Longer decay in percussive repeats that uniquely collapse into themselves as they grow throatier. Hazy, lush sound that's both full and somewhere between hifi/lofi, and saturates into synth pad type effects with open chord progressions and high feedback settings. It's really a challenge to find bad sounds in a good DMM.
ILFDD: More pronounced attack in repeats that progressively distort , darker+lofi voicing, much longer delay time, versatile and extreme with the switchable modulation w/both depth & speed knobs. With modulation it has a good amount of the DMM's character, without [it] engaged I'm reminded of my old DM-2's behavior.
They're set (ILFDD ~600ms, DMM ~300ms) to be used in series where they produce a sound remarkably similar to a RE-201...and the momentary oscillation makes for swells and drives the DMM into rhythm machine territory.