I tend to gravitate to cheaper pens including a lot of Chinese-manufactured versions of more famous pens (clones / knockoffs), and thought it might be interesting to post some of them?
This one is one of my favorites: the Wing Sung 601. This pen comes in a variety of different plastic-body colors, which are also great - I have a burgundy version of this pen which works beautifully. The style and hooded nib are clearly an "homage" (read:clone) to the Parker 51. The history between Parker and Wing Sung is interesting and complex, and has been described in detail elsewhere with respect to Hero (which owns Wing Sung.
There is a great review of this pen at The Gentleman Stationer. The version that I have is a "Flighter" all steel body (around $25 on eBay, a bit more expensive than the plastic body version but not by too much).
The pen's big highlight is the vacumatic filling system, which works beautifully. The body of the pen acts as the reservoir allowing it to hold a ton of ink for a pen this small. I find that the pen writes very well and is tremendously reliable - never a hard start, and the construction of the pen and hooded nib have meant that there are no problems whatsoever with drying out. I've picked this pen up after a few months of no use and it writes immediately. The steel body adds a little heft, which I like, and the pen is extremely durable. The hooded nib also makes for a good "stealth FP" experience, if you're in a setting where you don't want to draw too much attention to the pen.
All in all, it's a great pickup for not a huge amount of cash, and has found it's way into heavy rotation for me.
Just looked up the ink capacity which is 1.8 mL (!) - pretty nuts in a pen of this size.
Thanks for pointing out the difference between the filling systems. I hadn't realized that the 601 uses a piston type system (some reviews online suggest that the earlier 601s used the latex sac method, but it seems like the piston will not require as much maintenance over time and hopefully improve the pen's durability). This post has some good pictures of a demonstrator version to show what that piston system looks like:
And this video shows them in action.