Costa Del MarC-Line Retainer

Are these straps adjustable? I know that it says that thay are in the info, but some reviews say that they aren't.

What is the difference between C-line and C-mono?

How long are they?

This add is deceiving, picture in add indicates 16" length, after placing in cart, item then lists as 13" ultra thin retainer? Need 16" or longer ???