This brush is amazing. With a simple press of the button the bristles retract to easily clean out built up hair. Great price at $15. Great for long hair dogs. We found it best to work in sections and use short brushes to really get the undercoat. I was surprised with the fine metal bristles that they didn’t bend at all. It’s amazing how not a lot of pressure is needed to get thru basic knots. It also has a wide surface for quicker jobs. 
However we found that this is not the best for short haired animals. It just will not get through thick matting they have. Another thing is the bristles are a bit sharp for animals that might have sensitive skin. Overall I highly recommend this for any long-haired dog owner.