USE
I use the D.Loop for my bass pedalboard, for multiple purposes. I use one loop for the pedals, to switch between clean and FX bass sound. I use the other loop to switch between my bass and my bass synth.
BUILD QUALITY
Sturdy, sure can take a beating. The switches are literally noiseless (only noise I heard during switching came from a faulty power supply for one of the FX pedals). The switches are sensitive, no need to step on them very strongly (they are very sturdy and can take abuse though).
OPERATION
You can connect two effect loops to the pedal (or, as I did, any other instrument you'd like to use on the same channel as the original input). You can use these independently and simultaneously. You also have a buffered boost function which is great for solos etc. You can set how much it reduces or boosts the volume.
The pedal has several operating modes, button functions etc. can be programmed.
Sound quality is amazing, meaning it is as noiseless and is as transparent as it gets (meaning, sound quality doesn't degrade at all when you go through this pedal).
It can also work with other Lehle pedals via a special connection but I never used it this way so I don't know how well it works (judging by other Lehle units it's probably flawless).
SUMMARY
For me, switching between loops doesn't get better than this.