Learn Dutch: Hun product is duur. Ons product is daarentegen goedkoop. - Their product is expensive. Our product, on the other hand, is cheap.

Daarentegen is an adverb. While you can put it at the beginning of the sentence, doing so triggers inversion where the verb comes before the subject (Daarentegen is ons product goedkoop). It is often more natural and common to place it right after the verb, similar to saying "Our product, on the other hand, is cheap" in English.

Could I use echter instead of daarentegen in this sentence?

Yes, using echter (however) would be grammatically correct (Ons product is echter goedkoop). However, daarentegen is a stronger choice here because it specifically means "on the other hand" or "by contrast." It perfectly highlights the direct comparison between two distinct subjects (their product vs. our product).

Could I use integendeel in this sentence to mean the same thing?

No, integendeel (on the contrary) doesn't fit here. You use integendeel to contradict or deny a previous statement about the same subject, not to compare two different subjects. For example, you would use it if you said: "Our product is not expensive. Integendeel, it is very cheap."

Why do we use ons product instead of onze product?