Where the motor sits in a vibrating sleeve
Compare removable inserts, open grips and motors built into a housing.
Identify what the listing actually includes
Find the package contents and identify the sleeve, motor, caps and charging cable or batteries. The Mistress Paris listing explicitly names a removable egg and batteries sold separately. The PDX Elite listing names a bullet. Ask how it fits into the sleeve if the listing leaves that detail open.
With an integrated design such as the Arcwave Zing, the number of motors and the number of patterns describe different things. Read the controls section of the exact manual to find out whether you can select each motor separately.
Compare access before you compare mode counts
An open grip can expose more of the sleeve surface for inspection. An enclosed sleeve can have different caps, removable parts and care steps. Ask which components can be replaced independently if you expect to keep the housing for a long time.
Separate vibration from other powered functions
The Torrent listing describes air pressure as well as vibration. If you specifically want a unit that drives its own movement, see the motorized motion and stop control guide for the difference between vibration, rotation and thrusting.