The pen is not compatible with the Asus Vivobook S 14 Flip. This laptop supports the ASUS Pen 2.0 (model SA203H) with Microsoft Pen Protocol (MPP) 2.0, while the SA300 pen was developed for USI 1.0 devices such as the Chromebook C436 and is not suitable for the Vivobook S 14 Flip.
No, according to my research this pen is only compatible with these models: C536, CT300, Chromebook C436. This stylus should be compatible: ASUS SA200H Stylus
According to my research, unfortunately not, no. This one should fit: ASUS SA200H Stylus
The manufacturer's number leads to the manufacturer's page, where "ASUS Vivobook Flip TP412FA" is listed as a compatible product. And the two buttons on the linked pen are "erase" and "mouse click"! :-)