In the end, with ANY rollerball/ballpoint/pencil, if you pay more than $5 for it, you're essentially paying for just the shell...the refills are still the same across the company's entire lineup, whether it be their $5 model or their $500 model. What this guy did is nothing new...I've been doing this type of modding for most of my life...find a refill you like, and find ways to fit it into a "shell" that looks pretty. I have a huge bag full of refills from just about every pen refill manufacturer out there for exactly this purpose. Montblanc is hardly the last word for a smooth ballpoint refill...get the 1.0mm Jetstream for $2, there's just about nothing out there that can touch the Jetstream for a nearly frictionless sensation when writing.
Ever since I got bitten by the fountain pen bug, I've been pretty reluctant to spend a whole lot on any ballpoint or rollerball...with a high end fountain pen at least a good chunk of your money's actually going into a unique, one of a kind part, the nib, and not just another cartridge holder. Nonetheless, for most of my daily writing, I still use rollerballs or ballpoints, in particular the 0.5 Energel needletip refill fitted to some high end "shells" (I've gotten it to fit into a Montblanc Starwalker fineliner with some minor modding, works very nicely and has become my favorite daily pen). Fountain pen ink just takes too long to dry and the types of surfaces one encounters in the course of a day is way to diverse to trust to a fountain pen.