I use polarisers and grads in my colour work. They can both look fake. They can both look good. Depends how and when you use them.
A polariser can look pretty terrible if you over-polarise or with a wide angle lens, or ( in my opinion ) if the scene is largely dull though with a bright sky.
A grad can look unnatural if you forget that a sky is generally about a stop brighter than its reflection in water; or if you use a grad hard enough to leave a visible line across the photograph.
You need both in your bag and the time to look closely at the effect created to assess which if either is right. All of the usual fault modes are visible ttl. with care.