Just wanna throw my two cents in…
I have suffered from a frenulum injury, and has since been rather sensitive around that area. The rotary inner sleeve of the Syncbot directly stimulate that part. Which is not very comfortable to me.
This rotary sleeve contributes to a great portion of the stimulation. Should I disable the rotation aixs, all that left is the up-down movement and contraction. The vaccum these creates is very comfortable, but is not stimulating enough to push me over the edge.
This is just my experience and as mentioned I have issues myself. Though I’ve still enjoyed many other toys I’ve collected over these years without issue (even the LEGO® Sleeve works for me).
I just hope Syncbot release a few Scabbard variant with milder textures so I could comfortably shove my member into this device knowing it won’t come out sharpened.