The eye thing might be from tadpole, I kind of headcanon that he had similar glowing eyes like his brethren before getting tadpoled, I mean it already makes it so that the normal vampire rules don't apply to him, like running water, sunlight, OCD need to count stuff, religious symbols, needing an invition aka normal vampire stuff.
Most people don't know about the Vampire OCD thing, like if you're trapped in a corner with a vampire, you just need to throw some rice grains or coins, they would stop whatever they were doing, even hunting you and start counting the stuff you threw individually like one by one, it even overrides their self preservation instincts, since if you threw a lot, they'll still be counting after sun is done rising, you could potentially trap a vampire on a beach just by throwing sand at them.
The eyes, among other things was likely from the tadpole, or more specifically the netherese magic imbued tadpoles which blocks out Cazador and messes with other magic stuffs. It also messes with Wryll (and Gale ate a netherese orb even before taking a tadpole to the eye which effed his magic-ing up bad turning them into level 1 punching bags). If anyone paid attention after the non-ascension, all the other spawn lost the eye thing after daddy Caz bites the bullet.
That would have been such a cool RP option to have in the game!
But indeed it looks like there are no downsides for Tav, I guess Astarion's blood is OP like that. Tav can probably enjoy all the benefits of being a living vampire as he does (as long they stay near him), just doesn't gain new abilities like summoning creatures, and so on.
The Ravenloft style vampire bride / groom theory suggests Tav doesn’t actually need Astarion for those benefits, and Astarion is just gaslighting to better control Tav, since they may actually not be under his compulsions, even in the end scene (though they’d still be bonded and couldn’t hurt the other without hurting themselves).
Well, intended or not. Ascended Astarion is a corpse in my last run, and looks like Vampire Spawn-Tav didn't need him at all. I broke up with him and took him back to meet the Gur. But yes, Astarion should/would know that as long as the Tadpole exists, he could lose control. Tadpole gone, then TAV is his until he decides otherwise.
