The short answer
The $92.25 tumbler is the best-rated thing here at 4.7 / 5. The two weakest are the earbuds at 4.0 / 5 and the $233.08 fitness band at 4.1 / 5, and part of what that band tracks sits behind a subscription. Those facts are most of the decision.
If you buy one thing off this page, make it the $56.99 power bank. It is the cheapest, it rates 4.5 / 5, and it is the only one here that solves a problem you have already had this year.
Amazon finds is a category that runs on other people's enthusiasm, so it rewards a cold look at the numbers. Six products, $56.99 to $249, and what each one is actually for.
The one I'd buy first: the power bank
45W output refills a phone fast and will top up a small laptop in a pinch, with 20000mAh to spread across a weekend. It is chunky for a pocket, which is the trade for the capacity.
45W is the number that matters. Most cheap banks trickle, and a phone that gains 12% during a train ride has not really been charged. The chunkiness is real and it is the trade you are making for the capacity, so this lives in a bag rather than a pocket.
The highest-rated: the tumbler
Keeps drinks cold around 11 hours and hot about 7, with a tapered base that fits most car cup holders. Filled with ice, all 40oz of it gets heavy.
At 4.7 / 5 this is the best-rated product on the page, which surprises people who assume the hype is the whole story. The honest catch is weight: filled with ice, 40oz is heavy enough that plenty of owners end up using it at a desk rather than carrying it.
The e-reader
Waterproof, glare-free in direct sunlight, roughly 10 weeks per charge. Locked to Amazon's bookstore, so library and Kobo files need converting first.
Ten weeks per charge and readable in direct sun are the two things a phone cannot do, and they are why this still sells at $249 against a tablet that does more. The lock-in is the thing to weigh: library books and Kobo files need converting, so a heavy library borrower should think twice.
The hair tool: who the barrel actually suits
Dries and rounds your ends in one pass, so there's no juggling a dryer and a brush. The barrel is big, which makes anything shorter than a bob awkward to wrap.
The barrel size is the whole story. On long hair it dries and turns the ends in one pass, which is the job. On anything shorter than a bob it is awkward to wrap and you will fight it, so this is a length decision rather than a price one. If you are choosing between this and a proper dryer, the four tool types is the shorter way to decide.
The one to think hardest about: the fitness band
Heart rate, sleep stages, and stress tracking on a band you charge about once a week. Some of the better data sits behind a Fitbit Premium subscription.
At 4.1 / 5 it is rated below everything else on this page bar the earbuds, and the reason is not the hardware. Some of the data people buy it for sits behind Fitbit Premium, so the $233.08 on the listing is not the whole price. Work out what a year of the subscription adds before you decide, because that is the number that makes or breaks it against a cheaper band.
The earbuds
The Soundcore Liberty 4 Pro sit at $174.97 and 4.0 / 5, and they have their own comparison here against headphones costing more than twice as much: Sony WH-1000XM5 vs Soundcore Liberty 4 Pro.
What this list is and isn't
Every figure above is what Amazon Australia is charging today and what its buyers have rated, and prices in this category move more than any other on the site. What it is not is a month with each product in my hands. Where that matters most is comfort and build, so read the one-star reviews on the listing before you commit.