Worthwhile smoothie add-ins?

I’ve started making simple smoothies for a quick on-the-go breakfast (frozen mixed fruit + plain greek yogurt + water.)

I see many “superfood” add-in ingredients recommended - flax, bee pollen, acai, cacao, hemp (that plant seems to magically be the hippies’ answer to everything, LOL), chia, goji, maca, spirulina, etc…

I don’t know what half of these things are, and suspect a lot of hype and/or “woo” involved with them (“fat burning”, etc.) - are there any that are truly nutritionally useful? Ideally they would increase satiety, and be complementary or neutral in flavor/texture.

Aggregates and summarizes research on supplements.

Just to get you started-Spirulina.