It's cheap, totally reliable, and the nib is a really interesting one.
Visually - the nib casually resembles an uncovered 45, and it's nice to see some heritage. I also like the design evolution of the clip, and the straight sided cylinder is as distinctive and recogniseable as the 51's hooded nib was when that fist came out. The colour and design variety make the choice outstanding, and having a pallette of Vectors for each ink colour (for instance) would be a snip. Oh, and the Vector Flighter looks really cool posted.
Nib - In my experience, the nib (though it's nail-hard) is very, very smooth. I've never had skipping on any of the three vectors I've used. I can get nice ink shading using it, too. Sometimes it feels like using a paintbrush next to my esterbrook 9128. Also, it is simply immune to drying! I've left that nib uncapped on my desk for an hour, then picked it up and started writing with it first stroke! Great when you alternate pens for colour contrast.
Changing a nib on one of these is really easy - they just slide out, as easy as Lamys (there's a thread on it in the repair forum somewhere - worth a search if you're interested). You can mount spare nibs on them for fun with almost no hassle. Section units are two a penny in the Parker calligraphy sets (which come with four sections, four italics nib types). Perfect for finding out how these things look, easily fiddling, and playing Mister Nibmeister.
One other thing I wanted to metnion is that it's just perfect for ink testing. Have you ever dipped one of these things? They hold half a bottle in the feed - I just wrote almost 3 A4 pages with one dip. Three pages!
Even if they're not as perfect as a nice 51, as historical as a Lucky curve, or as luxurious as a Ciselie, these guys are a great school pen, and make a great tool for the FP collector.
...but I guess...YMMV
