I have not....however Ill still chime in with a disclaimer. I checked this pedal out, and here is a quote from their advertisement.
"With a full-frequency response, minimal compression and zero tonal coloration"
One of the reasons that the OD 808 does so well with a recto(in most peoples eyes) is because there is a pretty noticeable low cut present with that pedal. This in effect drastically tightens the amp up. If the 820 works as claimed, Id assume the full frequency response comment means that you dont have all of the bass loss present. In terms of tonal coloration.....if anything the 808 definitely adds a hint of midrange, which is also beneficial. These two factors of the 808, although not great in all situations, definitely improve what some folks perceive to be a shortcoming with the recto series.
if the 820 works as claimed with no tonal change and a full frequency response, you lose that mid flavor and low end cut that make the 808 popular.
But.....I cant say that the 820 doesnt add some other good elements (having not actually used it), but for the most part my gut tells me the 820(albeit maybe a more transparent pedal) wouldnt be as popular with a recto.