Try opening the center grooves on a Jinhao feed and dropping a Zebra G disposable flex nib in there! Cheap flex fun, with a bit of frustration possible. 
Helps to prime the nib when you first start writing.
I saw the three 159’s spring color bundle on Amazon for $12.99 prime and had to try it out!
This one was with Noodler’s Proctor’s Ledge ink which is a bit dry.
Line the vertical groove on the nib up with a feed gap.
