This Spring, I picked up a couple Windsor Newton Series 7 brushes. They're amazing brushes, but they were expensive, so I picked up a few products to keep them clean and in good condition. Now that I've spent some time with them, I figured it would be a good time to write up a review.
The first product I picked up was Windsor and Newton Brush Cleaner and Restorer. This is a thin liquid that you soak your brushes in to remove paint. It does a good job of cleaning brushes with dried on paint, even paint inside the ferrule. It's slow working though, and I found the best results from soaking the brush bristles overnight.
While it's great for cleaning really dirty brushes, it doesn't work well as a routine brush cleaner. It takes too long to be worth using after every painting session, and it doesn't seem to condition the bristles at all (by which I mean keep them flexible and pointed).
Looking for something to fill this niche, I picked up "The Masters" Brush Cleaner and Preserver. It looks like a tin of show polish, but contains what is essentially a soft soap. You clean your brushes by wetting them and drawing them backwards across the surface of the soap, then rinsing them out. This won't remove dried on paint like the Windsor and Newton Brush Cleaner, but it is good at removing any lingering paint right after you finish painting.
A bonus is that it works well as a brush conditioner. Once your brushes are clean, wet them and run them a few times across the soap, giving the bristles a thin coating. Then work the bristles to a point and store your brushes. This keeps the bristles pointed, and all you have to do to remove it is rinse the brush before you start painting again. It's kept my new brushes in better condition than ever before.
I heartily recommend "The Masters" Brush Cleaner and Preserver for routine brush maintenance. It really is great for it. The Windsor and Newton Brush Cleaner and Restorer is more of a niche product. It cleans very dirty brushes, but you should never let your brushes get to that condition in most circumstances.