I like modding my TWSBIs it would seem.
This is the pink TWSBI Eco, but I have modified the feed (read: cut) so that it would work with a Mabie Todd No.2 flex nib (made in England, for those interested, not New York, US as it makes a difference). You can't press it to total limits, but it works impressively well!
Currently inked with Diamine Rockin' Rio. This is from their Shimmertastics range and pairs phenomenally with the vintage flex. I can clean out if you want to use your own specific ink - drop me a message!
£50. This includes the mod.