as far as i have experienced first hand and heard from others, both are good for protection if put on a nice clean surface. they dont completely stop rust, it will slow it down some (little). i have heard also that they are not extremely porous but that they will absorb some mudd and gunk and its hard to get it complletely clean again! the only things that can be applied to rust and will completely stop it are por 15 and RE.
'95 grand 4.0L, 4.5" RE, 32x11.50" BFG km &'86 1/2 CJ7 258, d300, d44 rear, 4" superlift, 33x12.50 BFG km&90 xj 3" lift 31" mud terrains