The reason Iroha does not call this product "penis ring" is that due to their elongated and thin design these vibrators are gender neutral and versatile. They can be enjoyed solo or with a partner.

Solo use: Insertable bullet vibrator, attach to finger, attach to Insertable Pleasure Items
Partnered Use: Attach to strap on dildo, attach to finger, attach to penis shaft

They are quite powerful and come with 5 strength and 2 vibration patterns. TENGA SVR + is for those who prefer even much more powerful vibrations.