Tangible makes care products for specialty contact lenses, and one of them exists for a very specific reason. Hydra-PEG is a surface coating applied to some rigid and scleral lenses, and it is not compatible with everything on the solution shelf. Using the wrong product on a coated lens can shorten the life of the coating you paid for.
Start with whether your lenses are coated. If your fitter mentioned Hydra-PEG, or your lenses arrived with a note about compatible solutions, Clean and Boost are the pairing built for that situation. If the lenses are not coated, Clean still works as an everyday multi purpose solution across lens types, which is handy in a household where two people wear different lenses.
On sizes, the 12 oz bottle is the one for the bathroom cabinet and the 3.4 oz travel size clears carry on liquid rules. Fill is a separate product from Clean and does not stand in for it: saline fills and rinses, it does not clean or disinfect. If you are not certain what your lenses are coated with, the practice that fitted them will have it on file.