The Da Vinci Maestro travel pocket brushes are what I use besides the Holbein waterbrush.
The brushes are available from size 1 to 12.
I bought four of these in various sizes, 2, 4, 6 and 8. The one I use often is size 6. Size 8 is a huge step up from 6, which explains why it cost almost twice as much.
These are the 1503 series of travel brushes. Do not confuse these with the 1573 series which are made of synthetic hair marketed as Cosmotop Spin.
They are made from Winter Siberian Kolinsky Red Sable hair. That's top quality hair. The hair is extremely durable. I've used them for around 9 months and they don't show any signs of wearing out. Just for comparison, during the same time, I've worn out three waterbrushes with synthetic tips.
I like the brush design because it can be collapsed into a smaller size. The white portion above is actually the barcode sticker which has worn off over the years.
The cap protects the brush tips while you're traveling. At the top of the cap is a tiny hole for ventilation. However, the hole is too small to dry the brush fully so you need to dry it out a bit first before putting the cap on.
The black plastic is really hard and well made.
Depending on the size of your watercolour box, you might be able to fit one in also. They are great for traveling.
The brush tips can taper into a firm sharp point, even for the biggest one. They are easy to control and can hold more water than synthetic alternatives.
The main advantage compared to synthetic brushes is the water comes out of the brush easier. And you can flick the brush hard to force out the water, after that it's commonly used to collect pools of water that might be on the paper. Synthetic brushes are not able to do that.
Another thing is the brush hair will retain their shape well after each use.
However, when they dry completely, they tend to fray outwards. Just saying. All four of my brushes do that.
The sable brush is able to create an even flat wash effortlessly. That's the reason to go for a traditional brush. The waterbrush wash by comparison is patchy and you need really fine technique to get an even flat wash.
Sable brushes are not cheap. However, they are still amazing value for the money simply because of the durable high quality brush hair. They can last a long time with proper care like simple cleaning with water.
Highly recommended to all who uses watercolour.
Find more reviews at Dick Blick Art Materials (US) | Jackson's Art Supplies (UK)