Yeah, it's a modulated delay. Not sure what sort of modulation it does to the repeats though. The Deep Blue Delay also uses the PT2399. What I like about it is that the original signal doesn't go through the digital chip, only the repeats do.
I have started to get a handle on that by studying drive pedals, identifying the common elements and differences and so on. For myself, it's not the circuit complexity or understanding how it works that puts me off the larger stripboard builds. It's simply the concentration needed to get it right. Maybe it wouldn't be so bad if I relax my expectation of how long a build should take.