There are bunch of these, aside from their standard product sales that carry no penalties for accessing them, MAGMA can provide heavy weapons for XCOM, but can also trade with XCOM for much more specialized equipment, these deals come with a massive hit to your score, permament bad events further tanking your score for the rest of the campaign and also missions that exist due to XCOM trading the tech.
What is also bizzare is that you can share/tell them to fuck off about sharing tech you have no way of actually making, you can give them access to alien gardens, but you dont even have pulse weapons, so you give them something with negative 1500 points + slander events for fuckall.
So lets list them
1) Tritanium ammo share
- Prior to earlier versions of the mod, was way easier to access and benefit from
2) Alien Garden share
- Completely useless without the pulse rifle tech
3) Elerium battery share
- Completely useless without terramite share
4) Terramite share
- Completely useless without the battery share
5) Elerium explosives
- Only one product, at the point where you have elerium explosives, you probably have bigger explosives already.