Eco? Is it especially friendly to the environment? Only in the same way that any refillable fountain pen is - you won't be throwing the pen away, just buying more bottles of ink when you need them, which are usually in recyclable glass. So, yes, but that's not the 'eco' in the TWSBI Eco. It's called the Eco because it's so economical - an amazingly good price for a high quality piston-filler fountain pen.
The filling system is quick and easy to use, and holds plenty of ink. The clear barrel means you know well in advance when you're starting to run low on ink, too, so you don't run dry unexpectedly.