As per my favorite fountain pen, it has all to do with looks - the Pilot M90. Here is the original description from our website back in 2009 when they were issued:
In celebration of Pilot’s 90th anniversary, Pilot is pleased to announce the launch of the Limited Edition MU/M90 Fountain Pen. The MU/M90’s cutting edge design is like no other. Made of durable stainless steel, the sleek, streamlined body features an integrated clip with an attractive sythetic blue stone embedded atop. The MU/M90 comes in a fine or medium, one-piece steel nib with blue ink cartridge and a converter. The pen is merchandised in a commemorative 90th anniversary gift box.Limited to 9000 pens worldwide, but only 1175 in the U.S. 4 11/16" closed, 5.5" with cap posted. Limited three year guarantee.
Both my wife and I kept one of these babies. We fell in love with their unusual size and shape - that sleek, streamlined look just called out to us. So without further ado, here it is:
These did sell out in a heartbeat and are now usually listed on eBay around the $500 mark. However, if you like this pen you might want to check out the Pilot E95S which came out in the last quarter of 2014 and shares similar lines and proportions. However, rather than the integral nib and body design of the M90, the nib can actually be repaired or replaced if damaged on the E95S.