To begin with, I play Orange amps (chiefly a Dual Terror) so that is the basis for my review. I have tried a lot of overdrives and a couple of other ODs/boosters have made the cut in the studio as a contrast to the OD808, but this one is my absolute go-to.
The main thing I use it for is to have the amp on a heavy crunch (gain around two thirds to three quarters) and add the pedal into the front to push and tighten the sound - gain at 9 o'clock, level right up and tone between 1 and 2 o'clock. Obviously it's great going into a clean amp for more bluesy sounds, but there are plenty of other reviews covering that. Used the way I use it, the OD808 gives a fabulously gritty, smooth, and very musical overdrive by pushing the amp; the Dual Terror is a very bright-sounding amp by nature, so it's important to not set the tone too high, but it's awesome through darker sounding amps like the Dark Terror to get those snarly mid-range tones to come through and make the sound punchier and less muddy.
Build-wise it's all good, not amazingly heavy but definitely robust and reliable. Something went wrong with my original one this year (2022), but the awesome folks at Thomann simply sent me a replacement (first-class customer service as always). I couldn't find anything online about the problem I was encountering, so I guess it was just a freak occurrence and I wouldn't hesitate to buy another one if I needed it.
In practical terms, an important fact is that this little green box of WIN not only sounds great in the studio, but you can hear yourself really well on stage and in a band context with it as well.
It won't be giving up its place on my pedalboard any time soon :-)