There are quite a few of these 'nano' coatings around, from various makers. But for gtechniq- C1/C5 (they are the same) will provide the best protection. Apply with care though and take your time. It will last 2-3 years, depending on use, before you need to re-coat.
C2 is easy to apply, reapply and is cheaper. A coat will last 6 months, or easily 12 months with infrequent use. It isn't as hard as C1/C5, and so won't stop light scratches or protect as well, but it will still create a barrier, slowing down any reaction to the chrome plating.
Another option is to get another layer/s of plating added by a plating company here to your chrome. This will increase it's protection significantly, albeit an expensive option.
cheers, Steve