To NWH, yes it is stiff, you don't notice it on windows that sheet nicely, but on beading windows, it doesn't seem to splay the brush nicely, haven't taken off paint yet, well not really, and I've had terrible, no awful flaking frames, yes it does take the paint off a bit, but with an applicator and microfibre I used to take off as much.
No problem with spotting so far, I give the brush a good scrub with my hands from side to side after doing a window on a first clean, might help.