In this post to Johnny's Instagram page, the SL-20 can be seen in the upper-left corner of the image.

Noel Gallagher uses this pedal at least from 2015. It was featured in Premier Guitar's list of pedal he uses.

Some sources, however, say he used this pedal before 2015. This pedal could have been used in 2007. as this source cites.

http://the-noise-room.webs.com/

In this site, there is also a photo which is thought to be from 2007 Brits, possibly showing his pedalboard, where SL-20 is seen somewhere in the top left corner.

Photo 'table of tools' in 2010 Guardian interview with Eno

"And then the newest one would be the Slicer, which I picked up last year, right before we started doing the band, and I got that at, I think, Noisebug in Pomona in California, they always have a lot of great pedals, and [it] sort of goes further into like, the things that I was trying to do with the tremolo pedals, you know, but it has these cool harmonic things that happen in it that just don't happen, you know, with tremolos and, again, it's real versatile, and especially the fact that you can tap tempo the whole damn thing, so you can just sort of be changing it up all the time, so it's pretty cool" – Omar Rodríguez-López on the Boss SL-20 Slicer Twin Pedal, 0:55

En este video (minuto 10:49) podemos ver a Gustavo utilizando el SL-20 Slicer para crear texturas sonoras en la canción "Deja Vú".

OPN's SL-20 can be seen behind the SP-404 at 6:44 in this video.

Visible in Stompbox: 100 Pedals of the World's Greatest Guitarists, as can be seen in the quick browse video at 0:08.

17:13 Lissack always wondered how Johnny Marr got his tone for "How Soon Is Now?". He also explained in the rig rundown that he is using this pedal in conjunction with Line 6 M5 multi-effects pedal to create "Virtue" sound. He uses the tremolo setting on this pedal for the song.

At 17:19 of this "Rig Rundown" with Premier Guitar, Steve talks about the SL-20 saying "the other effects in that signal chain is this slicer, which is locked midi clock - which we have a Pro Tools rig out on the road with us. So, our drummer is on in ears, and he plays to a click. So I'm locked, no matter what tempo he's at, I can do slicing and stutter effects - live in time with my drummer which is really cool."

Boss SL-20 can be seen in the right-hand corner of the picture.

Before the Line Selctor and after the Vox wah is a slicer by Boss.

In this rehearsal picture, Toru can be seen with the distinctive Boss SL-20 pedal.