For the steels mentioned (carbon steels, simple stainless), a simple aluminum oxide pocket stone like the one demo'd above^ would likely be fine. The Gerber stainless mentioned is likely akin to something like 440A, which can be sharpened up easily on such a stone, as would also be the case for simple carbon steels. I generally favor stones like this for such steels, and/or something like a medium ('soft') Arkansas stone for additional refinement, beyond the finish left by the AlOx stone.
If choosing a diamond hone instead:
Bias the choice toward the finer end of the grit scale, for use on simpler steels. The suggestion of a Fine/EF diamond is pretty good. Since the steels being sharpened aren't very wear-resistant, i.e., they don't contain heavy amounts of hard carbides, it doesn't take a very coarse diamond grit to keep those in shape, or even repair some relatively heavy edge damage. A Coarse or XC diamond can leave edges on such steels very ragged, and will remove more metal than is necessary. Hence the recommendation to bias the choice toward the finer end of the grit scale.
The one caveat that might influence choosing a coarser grit, is if any heavy grinding needs to be done on larger/thicker blades, like big, heavy fixed blades. Overall, a larger stone in a Coarse/Fine grit (or even XC), would handle that work more efficiently, cutting grinding time down by as much as 3X - 4X. But, if the knives are small/medium-sized, and the upkeep doesn't involve heavy profiling or complete regrinding of bevels, then a pocket-sized Fine/EF diamond (600-1200) should be enough, and can leave great working edges as well.
ALL diamond hones should be used with a lighter touch than most would be accustomed to using on other stones. If used properly, a diamond hone will last a couple decades or longer; especially if it's just a maintenance hone for use on simpler steels.
