The Retainer is a different approach at Restoring/Retaining

DTR retainer sizes
Notched Retainer
Foreskin retainer  with notch

The bottom of the retainer is about 10 mm deep. This is about half the depth of a DTR bell.

Retainer spacer
Threaded retainer
Foreskin retainers  solid

Solid Retainer :
Uses: Retaining , Moisture retaining

Uses: Retaining

DTR retaining

The retainer sits on top of the glans and the shaft skin is pulled up and held in place by a gripper.

Retaining with weight
Retaining with Air

I found the Retainer to be a very useful device. It was able to hold on and not fall off the way O-rings can when you dont have much skin to work with. I did use it for Direct AIR and Weight when I was using those methods vs the DTR bell because it was a little more compact. I was able to sleep with the retainer in place however I would advise not to do this unless you have enough skin to work with and are comfortable doing so. Personally I feel an O-rings or the keeper are safer for sleeping and retaining.