A little update on that: My friend now also reached a stage where he wanted to buidl the rimatomic items. He could do so right away as i had unlocked them. He only had to do the basic rimatomics research of the main research, to be able to build the table and all other items i had unlocked before.

Once he also built some rimatomics towers, we basically had desyncs whenever a rimatomic weapon fired, or the shield got hit. No matter if it were his or mine.

Worked fine while only i had them. No problems at all. He even commented on how effective the shield was against enemy hits while observing one of my fights.