Learn Finnish: Tämä merkki on yhtä edullinen kuin tuo. - This brand is as affordable as that one.

It uses the pattern yhtä + adjective (edullinen) + kuin. Yhtä acts as the first "as" (meaning "equally"), and kuin acts as the second "as". The adjective stays in its basic form (nominative) because we are comparing two subjects in the nominative case (tämä merkki and tuo).

Why do we use yhtä here? Isn't that a form of the number one?

Yes, yhtä is the partitive form of the number yksi (one). When used in comparisons, it literally gives the idea of things being "of one [measure]" or "equally" the same.

I know the word halpa for "cheap". How is edullinen different?

Halpa simply means "cheap" and, just like in English, can sometimes carry a negative tone implying low quality. Edullinen is more positive; it means "affordable", "inexpensive", or "advantageous", implying you are getting good value for your money.

The English translation says "that one", but the Finnish sentence just ends with tuo. Do I ever need a word for "one" here?

No. In Finnish, demonstrative pronouns like tuo (that) and tämä (this) perfectly stand on their own. Adding a word for "one" (like yksi) to mimic English would sound very unnatural.

Can be used for any kind of brand, like cars or clothing?