What single item improved the quality of your life over you got it? (Buyed it/got as present/made it)

I can think of two benefits to an adjustable desk:

1. Better chairs at a lower cost. Most office chairs (and chairs in general) are designed for table-height desks, so you'll find a greater variety of multi-point-adjustable ergonomic options that'll improve your posture while seated. From a corporate perspective, these chairs are also more versatile when the office changes size or layout because they'll work just as well around the conference table as in the cubicle.
2. This one's purely a business reason, but also the main reason an office manager will have on their mind: the employee they hire to replace you might be a different height. Cynical, I know, but an adjustable height desk means they can accommodate anyone they hire now or in the future, and they've got to justify office expenses on a multi-year timescale

For you, an existing employee who already has a desk and chair you like, the adjustable desk will probably be a downgrade. For the office, it's a smart business decision that also means comfier chairs for everyone.

Yeah! I got this exact model from costco, which is a hell of deal in my opinion: https://www.costco.com/tresanti-geller-47%e2%80%9d-adjustable-height-desk.product.4000139627.html

But also, for a step up, I hear that fully makes really good ones: https://store.hermanmiller.com/standing-desks/jarvis-bamboo-standing-desk/2542428.html?lang=en_US

And if you're a little handy you can just buy the legs and make your own custom top

Not OP but my posture is improved and I move a lot more, so don't end a day of work feeling stiff.

It's not really about what a standing desk can do for you now, it's what it does for yourself in 10 years.

Alternating standing and sitting will help a lot. It's not that any given posture is bad, it's that any posture for a long period is bad. Don't just do the desk either, eyes fingers and legs too!