Here are some links to YouTube videos (with timestamps) that show Uni-Vibe / harmonic tremolo sounds.  


Pedal
Channel
Video (timestamp link)
Notes
Radius
Mike Hermans
Red Panda Radius (00:19)

RadiusThe Pedal ZoneRed Panda Radius - The Most Musical Ring Mod EVER! (00:36)
Random triggered tremolo.  The tremolo rate changes every note you play.
RadiusEmily HopkinsRed Panda Radius (6:31)Square wave LFO switches between slow and fast tremolo rates.
Radius
Tri Pedal Reviews
Red Panda Radius Demo & Web Editor Overview (41:55)
Factory preset 4; vibe/phaser