Is the Diamine Inkvent Calendar worth the price?
Diamine has one of the most economical costs per milliliter for a standard fountain pen ink. If you wanted a color that is part of their everyday range (like Marine), an 80ml bottle costs $17 ($0.21 per ml) A "standard" Inkvent color from 2021 costs $17 for a 50ml bottle ($0.34 per ml). A shimmer + sheen Inkvent ink costs $22 for a 50ml bottle ($0.44 per ml). Despite the higher price for the extra shimmer, it is still half the cost per ml compared to a Sailor Ink Studio color at $18 for 20 ml ($0.90 per ml).
The 2022 Diamine Inkvent Calendar contains a total of 318 ml of fountain pen ink (24 x 12ml bottles + 1 x 30ml bottle). Considering that the calendar contains a variety of standard, shimmering, sheening, scented, and chameleon colors, we could average the price per ml between the low end ($0.34 per ml) and the high end ($0.44 per ml). So, if we apply $0.39 per ml to the 318 ml total volume of ink, the overall ink value of the advent calendar is $124.02
While most producers of advent calendars will put less value into what's behind each door in favor of the elaborate packaging presentation, Diamine offers this calendar at a bargain of $115. Since the total cost of the calendar is less than the value (per ml) of ink inside it, you can consider the calendar a good value, especially if you enjoy sampling a variety of fountain pen inks.