Is buying a high-quality Montblanc Starwalker as ballpoint or rather as rollerball worthwhile, and are there objective writing advantages over inexpensive writing instruments?

The choice between ballpoint and rollerball is primarily a personal decision; collectors who themselves only write with fountain pens refer to personal comparison in specialist trade as the best decision basis. Factually: a Montblanc ballpoint refill is not in principle easier to guide than a good plastic ballpoint refill, and Montblanc ink hardly differs qualitatively from high-quality alternatives like Pelikan 4001. The added value lies above all in workmanship, material quality, ergonomics and haptics of the body, less in pure writing performance. Rollerball refills are shorter-lived and so more expensive in consumption.