Ok, redundant process manufacturing is an upgrade from WAR! which is generally, and quite rightly, considered to be entirely unworth its excessive price tag (2 slots and 100% to 200% of the base weapon price). It can be bought at ratings 1 or 2, and increases the gun's object resistance by that amount. When it is literally cheaper to carry a copy of your favorite gun around rather than make it marginally more resistant to some spells, the upgrade is unlikely to be a favorite.
However...
An Ares predator with RPM 2 weighs in at a healthy 1050 nuyen, which makes it a costly side arm. Why bother? Because improved invisibility suddenly needs 7 hits to overcome its object resistance and hide from it rather than 5. That means most mages are going to be overcasting, possibly several times, in order to get the required hits. It's also less likely that a mage has 7 initiations and extended masking than the 5 they need for a camera without RPM 2 (though 5 initiation mages aren't exactly common in the first place!).
Sure it's a narrow niche, but when it pays off it does so big time. And let's face it, who doesn't enjoy a mage's expression when you pop some caps through their supposedly impenetrable invisibility?