They have been found constitutional by the courts, though I agree with others that it is an unreasonable stop and search.
When you are stopped, you politely give as little information as possible. Don't drink and drive, tell the officer you haven't had anything to drink. They sometimes ask you to get out and do the tests, but if you're calm, clear and polite, you're usually waved past.
I also avoid driving when they are doing those tests.