I have too many TWSBI ECOs so I'm selling this one as part of trimming my collection. Like all ECO's, it writes nicely and holds a ton of ink. 

Here's a more formal description: 
The TWSBI ECO fountain pen boasts an incredible value with its piston filling system and affordable price. Like many other TWSBI fountain pens, this special edition ECO features a crystal clear acrylic barrel so you can see your ink level, and a translucent purple cap and piston knob. The pen cap has an inner cap to ensure a perfect seal when stored away. It is completed with silver trim and a silver stainless steel nib. This color is a limited production run.

TWSBI’s belief is that it is important to allow the user to disassemble and reassemble the pen and completely experience the traditional aspects of owning and using a fountain pen. These pens also come packaged with a wrench and silicone grease. Neither of these accessories are intended to be used immediately, as they are for long-term care and maintenance

Product Specifications
Capped Length: 5.45 in.(138.4mm)
Posted Length: 6.6 in.(167.6mm)
Length of Body: 5.125 in.(130.2mm)
Length of Cap: 2.375 in.(60.3mm)
Diameter of Body: 0.5 in.(12.7mm)
Diameter of Cap: 0.6 in.(15.2mm)
Weight: 0.45 oz.(12.76g)

Body Material: Resin
Trim Material: Chrome Plated
Section Material: Resin
Nib Material: Stainless Steel

Fill Mechanism: Piston
Cartridge Type: Bottled Ink
Ink Capacity: 1.75ml
Cap Rotations: 1
Cap Type: Threaded
Postable: Yes
Demonstrator: Yes
Clip Style: Spring Metal