Maybe I can help with some personal experience, since I bought a bigger stylus just recently. My intial thought was that it would be great to have a bigger stylus in order to write something down. However, I normally read technical texts on the M92 and if I want to "scribble" something into the text, it is normally just some words, not many sentences. For such a task, the smaller stylus is sufficient. Using the "annotation"-tool, the situation is no different. The only situation in which I would definitely prefer the bigger stylus is writing a lot of text in the scribble application. However, I find the scribble application less useful than initially thought (only one shade of grey as "colour", no eraser tool, having to use the device's buttons pretty often...), rendering the bigger stylus less of an improvement than expected.
Another aspect to consider is that the small stylus fits into the M92's case. A bigger one does not. Carrying the M92 around a lot, I tend to leave the bigger stylus at home more often than not.
As soon as there is an eraser function that is tied to a bigger stylus (many of them have a sort of "eraser" part on the back), I'll definitely go for the big one. Until then, the improvement in comfort is not as significant as I expected.
I hope this helps.