I'm building a live set up for a theatre production and am running a mic and synth from a mixer into a Digitech DL-8, also a delay & looper, and then to the Flashback. First, both pedals can receive line level inputs with no problems - the Flashback automatically adjusts itself to line level inputs. The DL-8 is a really interesting delay in that almost all the delays create dramatic modulation when you tweak the Time knob, so I use that with the Repeat turned all the way up to create sustained warbly effects. By contrast, the Flashback sounds warmer and creamier and the Time factor has much more subtle artifacts (even in Tape, Analog w/ mod and 2290 w/mod). The looper runs simultaneously with the delay (one of the main reasons I bought it), so you can record a processed riff into the loop, change the delay (say, you record first loop with Analog, and switch to Reverse), then add the next layer with Reverse effects, etc etc. I don't use the tap tempo because I'm creating more ambient soundscapes, but it's handy to have when I'm occasionally working with arpeggios and more percussive sounds. So, with two delays and loopers with different characters I've been able to do lots and lots of cool stuff.
The only downside to the Flashback in my opinion is that the buffered bypass does not work in Looper mode, so - in Delay mode, you can switch the delay off and your sound will ring out with the delay. But when you stop your loop - it's a sudden cut. Same as when you switch from Looper back to Delay mode - the loop just cuts out abruptly. I'm planning to add a cheap reverb pedal to the end of the chain to fix that.
I've tested the EHX Memory Man w/ Hazarai and the Flashback side by side for over an hour at the store before picking the Flashback. The Memory Man is a different beast sonically, and in a really cool way, but I also found it a bit harder to operate. The Flashback is SO straightforward and sounds absolutely fantastic.