My understanding is that the only currently available packaging is in 1 liter, which is not the same concentration as the original US packaging (493 ml or something like that). I still have a full bottle of the latter, and had been using it at the "unofficial" dilution H (1:63) which is twice the dilution of B. That has worked well enough for me, and I'll probably just stick to that as it takes me a bit further especially on 120 film where one needs a larger developer volume. If you work on 550 ml at 1:49, it will require 11 ml of concentrate, twice what is technically necessary per film. The obvious solution is to load two rolls onto one Paterson reel, which is entirely possible, but that means having to hoard films that require the same developing time. At dil H 10 ml gives me 640 ml of developer, and saves me a few drops of precious developer. It is very expensive to import liquids, so every drop helps.
For most films, HC-110 gives me a very similar result to Rodinal. However, Rollei RPX400 and Kentmere 400 fog something terrible in Rodinal, and are miles better in HC-110. I suspect that it might be true for some other emulsions also.
Why 550 and not 500ml? Which is what most tanks take, or 1L for a bigger tank.