I carry a chrome X-750. About six years ago I found it on the ground after a party, nobody ever came back looking for it, and it therefore became mine. Previous to this pen I had one of the bullet pens which I lost, therefore I think the pen-god decided it was time for me to get a new one.
As far as performance of the pen is concerned - it seems to depend on the ink cartridge I put in there. Occassionaly I get one that seems to "glop" the first time I use it after a time of non-use, but overall the cartridges (especially all of them recently) seem to not have this problem but instead deliver a constant and good amount of ink that makes for smooth and bold writing (I like the medium point cartridges).
In terms of size, this pen is excellent. It's real short when being carried but it can be elongated (by putting the cap on the back) when you actually want to write. I put it in my pocket and then forget that it's there until I need it (and occassionally don't recognize when it falls out of my pocket, which means that it's good at not being noticed, but bad about warning you when it's about to be lost!).
I don't think you can go wrong by getting this pen. It's pretty cheap for what it is and overall a good buy.