Let me break this down because it's actually an interesting choice with some deeper implications. The eye surgery option comes down to whether you value detection abilities over keeping your original eye (which some companions definitely have opinions about). Here's what's worth knowing: getting volo's special eye lets you spot invisible enemies within 30 feet without using any spells or resources, which is incredibly useful against things like hags and duergar lurking around.

The downside though, and this is important to consider, is that your eye will permanently glow blue (quite noticeable in conversations), and your companions won't be thrilled about the whole procedure. Volo actually disappears from camp afterward, probably because he knows everyone's mad at him. Something to keep in mind is that choosing this surgery means you can't make a deal with auntie ethel later for a different eye effect (her version gives intimidation bonuses but worse perception).

The tadpole in your head stays put either way, so don't worry about that part. If you're feeling squeamish about the surgery scene, you could technically just kill volo and take the eye (though that's a bit extreme). I'd say the invisibility detection is worth it in the long run, especially since you'll encounter quite a few sneaky enemies later on, but there's no pressure if you'd rather keep your original eye.

(Interesting side note: the ersatz eye's invisibility detection works exactly like the spell version, just without requiring any magic resources)