I like the M.P.F. Evolution Series by Peter Pizzi. It's a non-spring brush with replaceable brush tips.
Zahn sells their line of brushes and instuments.
http://mpfbrush.com/ http://mpfbrush.com/evolution-series-inspired-by-peter-pizzi/ I like the
line brushes, but the M.P.F. has a metal handle with serrations built in to lightly vibrate porcelain as needed.
I did not like their N.era brush.
http://smilelineusa.com/porcelain-brushes I have also tried and like the new Lay:Art brushes from Renfert. "Ergonomically contoured handle with a Soft Touch surface -
very light and well balanced for optimum handling. The three different sizes (#4, #6, #8) reflect the required amount of water and porcelain for each working stage. The fine design of the "slim" version reduces the moisture release and also facilitates a more delicate technique. The more robust "bold" brush in contrast enables higher moisture release and makes it easier to take up larger amounts of porcelain.Previously unknown long service life and resilience of the brush tip. One of the special features of the lay:art brushes: the tip is formed by many above-average, fine-tapering hairs of uniform length. This significantly increases the resilience and service life of the tip, as the mechanical stress is distributed over more hairs." The bruch tips are not repalceable.
http://www.lay-art.de/en/lay-art-style