Jaybird's $100 (£90, $AU150) Tarah is the entry-level model in its 2018-2019 line of wireless sports headphones, which also includes the($130, £90, AU$190) and ($160, AU$230, no UK pricing yet).
What's a little confusing is the headphones look pretty similar -- and all of them feature Jaybird's new buds and fins that provide a more secure and comfortable fit. However, they do have their differences.
Let's start from the top and work our way down. The higher-end Tarah Pro is supposed to be the best of the bunch, boasting an impressive 14 hours of battery life, magnets in the buds (so they can form a closed "necklace" instead of loosely dangling when not in use) and a "no stick" fabric cord that's reflective in case you happen to be running at night, as well as a couple of other small upgrades. The X4 doesn't have the magnets or the fabric cord, but its battery life is rated at 8 hours -- 2 hours better than the Tarah. The X4, like the Tarah Pro, also comes with a carrying pouch while the Tarah, reviewed here, doesn't.
Otherwise the Tarah's core specs are similar to its siblings. Not only is the Tarah sweatproof but Jaybird says it's fully water resistant, with an IPX7 rating, meaning it can be fully submersed to 1 meter for up to 30 minutes. There's also a fast-charge feature that gives you 1 hour of play time from a 10-minute charge.