Economy is one aspect, but there are others to consider, like shelf life and convenience, not to mention the effect the stuff has on the film (not all developers behave the same, or produce the same sort of result). Shelf life can affect both economy and convenience - if it's knackered before you've used it all, it costs more in the long run, and you have the hassle of buying it more frequently, and mixing it if it's a powder type.
HC-110 has a convenience consideration in that it's very concentrated and has a syrupy consistency. At 1+49, only 6ml is needed for a 35mm roll, and it's hard to measure that out accurately by pouring some into a beaker. The trick is to use a small syringe, but that means there will soon come a time when the syringe can't reach far enough into the bottle. That's solved by decanting into a smaller bottle regularly and drawing off liquid with the syringe from that. And you need to add the syringe to the stuff to be cleaned every time you dev a film. It sounds like a hassle, but it actually isn't once you get used to it. If anything, it's easier to be accurate quickly with the syringe - can't over-pour into the beaker and then have to put some back into the bottle. And I just wash bits as I go, between tank agitations.
The main reasons I picked HC-110 were the long shelf life, and the fact that Ansel Adams used it (if it's good enough for St Ansel, it's good enough for me). I'm not especially interested in trawling through multiple developers to see what the subtle differences are - as long as the stuff produces decent negs, I'm happy to be pragmatic about it.
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