I wanted a roll-out piece in order to access the corner space. Ikea doesn't make castors for the Akurum line of kitchen cabinets. I bought the casters at Ace Hardware. I think they were rated for 75 pounds or something. This small cabinet wasn't intended to hold anything too heavy, and the butcher block top is not that heavy. I needed casters small enough that the cabinet would still clear under the counter top. I was all set to go to a specialty caster store, but the owners were on vacation and I was too impatient. I probably could have gotten heavier duty casters that would have been a small enough diameter.
I have braking casters for the front two, although I haven't needed to actually use the brakes -- it's been at least 6 months now I think. The weight of the cabinet seems to hold it in place fine if I am just opening drawers. You may notice I got a different style than the rest of the cabinets. That is because the casters are shorter than the legs (so that the cabinet will roll under the counter top), cabinet doors/drawer fronts don't line up. I thought it would look strange for 2 Adel style cabinets to be side-by-side and not line up, so I went with a totally different style (ABSTRAKT high gloss gray).
One of the casters is screwed directly to the cabinet. The other 3 are shimmed so that the cabinet sits level in its space. My floor is not at all level. This means that when the cabinet is rolled out, it is not level. But there's nothing to be done about that...my floor is the problem there. This has worked out very well, although I would be hesitant to try it on a bigger cabinet, or for a cabinet that was to carry a heavy load.