So about those, they were removed completely when engineering v1 was released.
You're right that when they were removed from sale those who already owned them got to keep them until engineering arrived.
I don't remember any of the effects being outstanding, more damage for reduced range or jitter etc, nothing that stood out at the time of engineering v1 that couldn't be replicated.
@Speedcuffs @Craith @Cmdr. Numa
See above
Edit: grandfathering engineering v1 modules was a mistake imo, they should have been removed
Edit 2: knowledge about what Stalker is referring to is becaue I had a couple of the special multicannons, which weren't that special really, just differently balanced. One of the things I liked about those weapons was there was a real tradeoff to the changes rather that just absolutely better like current engineering.