For me the Chubby 2 Synthetic now knocks every other synth I've used into a cocked-hat, kicks them down the road and piddles all over them. That includes a Men-U; Muehle M 21mm, Edwin Jagger L 23mm, Edwin Jagger XL 25mm and a 24mm Frank Shaving.
However, my first use was a disaster: too stiff, didn't splay, horribly “springy†and required enough force to splay that caused my hand to ache (I do have grip problems though). Based on comments from experienced synth users that man-made fibres will not change performance or behaviour with use I was disappointed. However, the BRUSH has changed, and very significantly, even if the fibres themselves haven't.
By the 4th or 5th use things were much better but still not to the same standard as a nice badger. Then I started mistreating it (relative to how I'd treat a badger). I ran the brush (knot up) under the hot tap (~60degC) at full chat and also used a hair dryer on hot and fast to open out the tightly packed knot. This brush now splays easily, does not feel at all springy, holds loads of soap and gives it up willingly and has tips far, far softer than any silvertip I've used. It's bloody great!
Also, I think the furore over the missing 4mm of loft is a red herring: my brush is 29/50, and I can't see the extra 4mm making much of a difference. I think the 2mm larger knot diameter (than specified) is probably more significant in creating a stiffer and, initially, harder to splay knot.
All in all, I'm now very pleased with the CH2S. However, I now need something suitable for traveling with… Mark?
Thing I dislike about it most?
It's a bit ugly.