We use 0.5 micron carbon blocks extensively and they work fine with booster pumps. The problems with filters from the big box stores are:
*specifications are often not provided, so you really don't know what you're buying
*these filters are intended for drinking water RO's, so they almost universally are not up to spec's demanded in this hobby
*You can get the filters at a better price at the vendors who sponsor R2R
Russ