I bought a Noodler's 'Nib Creaper' in Black about three years ago, out of interest really. At under £15 I didn't expect much but was very pleasantly surprised and I've used it hundreds of times since.
My preferred 'Daily writer' is a Parker 51 but I have found myself turning to this pen more often of late. There are two main reasons. Firstly, although my handwriting is still dire I am trying to improve it and the flex offered by the Nib Creaper gives more encouragement. Secondly the pen cost so little that I can treat it accordingly. That is not to say I abuse the pen but can happily stuff it in a pocket or drop it in the side pocket in the car etc. with gay abandon. I wouldn't do that to a Parker 51.
The pen is a real piston filler, not a converter, it works smoothly and takes a reasonable amount of ink, mine has never leaked.
The nib is steel, medium point, and has a really nice flex, not a lot but very easy and pleasant to use. I think it fits squarely into the 'semi flexible' classification. The pen is 13.3 cm. capped and 13.8 cm. posted, a comfortable if not excessive size. It has a chrome cap band and clip which carries the 'Noodler's Ink' name.
At £13.99 from a number of online outlets the pen is about the same price as a Parker Vector. There is nothing wrong with a Vector as a low price fountain pen, of course, but the Noodlers pen offers a piston filler and a really nice semi flex nib.
If you wanted to go up market a bit there is also the Noodler's Ahab, at around £20 you get the same works but in a bigger, flashier pen. The Ahab is a huge 17cm. posted, a giant of a pen.