I just visited their web site- the roller bushings are for springs, not king pins, which is what I was referring to.
In that application (springs) roller bushings would be a good idea because typical bushing mat'l is malleable and doesn't wear well. After a while the pin will wear as will the bushing and cause all kinds of havoc. Keeping them greased with grease designed to withstand high pressure would postpone but postpone only- the roller style will still require maintenance which includes proper grade grease- there's also load distribution to consider and they probably have a lot of testing to back their claims, but, still there is less surface area for weight distribution in the roller vs the malleable mat'l that runs the entire length of the pin. It would, I think, come down to maintenance.