Is 24 oz too big for a single latte?

It is on the large side for one drink. A 12 oz pitcher is easier to control for a single latte; the 24 oz size suits two drinks or a large batch of froth.

Can I put it in the dishwasher?

No. The listing says dishwasher safe parts: no. Hand wash and dry it to keep the mirror finish.

Does it work on any steam wand?

Yes. It is a manual pitcher with no moving parts, so it works with any espresso machine steam wand. You control the froth by hand.

What is the engraved scale for?

It marks volume inside the pitcher so you can measure milk before steaming. Engraved lines last longer than printed ones.

Is $20.89 a good price?

It is a low price for a stainless steel 24 oz pitcher from a commercial kitchen brand. Two stores list it new, so compare both before buying.

Is it worth it over a cheaper generic pitcher?

If you want an engraved scale and all-steel build, yes. If you only need a basic pitcher and don't care about markings, a cheaper one will do the same job.