Definitely invest in one that is made to measure. It's strikingly quick and easy to order one, but you will need a little (a week maybe) planning.

I remember getting into chastity early, around 2005, when the CB 2000s walked the Earth. I was fascinated with being able to control someone long after they left the dungeon. However, the CB 2000 being one-size-fits-all was always simultaneously uncomfortable (fine by me) and so loose it would fall off (unacceptable). I had to rethink chastity play when one fell off a slave on the subway, tumbling down his pant leg and on to the floor of line 4. 3D printing and the realization that penis sizes are different have done wonders.