I have long been selling my capped pens as "one, the other, or both" (RB, FP, or RB & FP). That way the customer could choose. Some really like the idea of a convertible pen. My observation is that it is not a pen collector who goes for the convertible option, but rather someone who enjoys pens, and is intrigued by the option to convert. I would typically price the upgrade to "convertible" as at least adding the cost of a second kit that I would pull the needed parts from. On a pen like the Imperial, that can be a little expensive, but was OK with customers.