The ups are really just related to Elin, if she's your favorite. Since it plays into the whole twin thing and being her portal buddy. Maybe Alaina too, if she's also your thing. But beyond getting more in-depth visions when meditating with Alaina. That's about it. The perk specific content isn't all that interesting otherwise.
The down side is that Elis doesn't seem to get better with magic. He gets a hard reset right before the coup. Powers that he showed earlier seem to have disappeared from his kit. He can't open portals, can hardly levitate a boot and it took him nearly dying to use fire magic.
It's seems to be intentionally nerfed for balance. As Mage Elis by all accounts should be pretty powerful. With his blood being from a powerful elven bloodline full of mages and such. But most events against him would fail too easily, if he was competent with it.