Does the vacuum insulation really keep drinks hot?

Yes. The double-wall vacuum seal is the point of the design and slows heat loss far better than a single-wall cup. Pre-heating with hot water before filling improves how long it holds heat.

Is it leak-proof in a bag?

The listing does not claim a leak-proof lid, so treat it as splash-resistant rather than sealed. Carry it upright in a bag or use a separate bottle for loose carry.

Can I put it in the dishwasher or microwave?

Stainless steel should not go in the microwave. Hand washing is the safer choice to protect the vacuum seal and the finish.

What comes in the two-piece set?

Two insulated stainless steel tumblers in green. Each is a separate cup, so you can keep one at home and one at work.

How does it compare with premium tumblers?

It covers the basics, insulation and a steel body, without the extra lid styles, handles or sizes premium brands offer. It is a sensible pick if you want simple insulation rather than features.