Depending on the cables you use, a Mooer might be almost as wide as any of Spencer's current small pedals. At least, my Polytune Mini is, with the cables I have. Top jacks for the win. I've checked out other cables too... George L's, Lava, etc. And they don't save enough room over my Planet Waves kit to justify changing everything out. If you're using those Hosa (?) flat pancake cables or maybe the new EBS ones, might make a difference.
5sg.
FYI, a mini pedal + EBS flat cables is still slightly wider than the 3Leaf You're Doom style enclosure.