What is a filbert brush good for?

A filbert has a flat head with an oval tip. It blends, lays down color and makes soft rounded strokes, which is why it sits between a flat and a round brush.

Are these brushes safe for acrylics and gouache?

Yes. The synthetic nylon bristles are listed for acrylic, watercolor, gouache, body and craft painting. Rinse them promptly after acrylic so paint does not dry in the ferrule.

How do I keep the bristles from splaying?

Wash with mild soap, reshape the head with your fingers and dry it flat or tip-up. Never stand them bristle-down in a water jar.

Is this set enough for a beginner?

It gives you several filbert sizes, which covers blending and general painting. You may still want a round for detail and a large flat or wash brush for big areas.

How does synthetic compare with natural-hair filberts?

Synthetic nylon is springier and more durable with water-based paint, while natural hair holds more liquid and releases it more smoothly. For acrylic and craft work, synthetic is the practical choice.