There is no reason to use meta-alloy HRP - even if you start fighting thargoids, caustic damage resistance is moot because a) it (the organic missile) is fairly easy to avoid, b) you can survive a long time with the effect on you, so finishing off the Thargoid is still an option, and c) if a and b aren't working out, you can cook it off by going silent running and heating until you get the caustic damage removed message.
The benefit from an engineered HRP far outweighs any consideration of the meta-alloy one.
Having said that, the powered module reinforcements seem alright if you have the power (all my anti-Thargoid rigs feature them) and the shield reinforcement packs are a game-changer on small-to-medium ships (for example I have a FAS and a Chieftain, both with >1k shields, with good damage resistances and an SCB).
tl;dr version, MAHRP is a waste of effort, but some of the other unlock-able modules are well worth it.
Oh, and P.S. Those who are saying the 4 AX weapon limit needs to go probably haven't had much experience with thargoids yet - they are creatures of habit, they move in patterns and have set-piece attacks, if you learn these, 4 AX weapons is enough. Plenty, in fact.
If you don't learn these patterns, you'll struggle with you and a buddy bringing 8 weapons to bear on the situation (or it's not what you do, it's the way that you do it).
The wets, if they get their way, will still die to thargoids even if they can have more than four AX weapons, the rest will probably not choose more than four anyway because there's other stuff, such as flak, that is not AX but works well on the tharglets and can go in the remaining slots.