I put two curious looking writing instruments through their paces:

S MOVE EASY = ink roller shaped almost like a banana with extra molds for lefties.
Result:
1.) The pen itself is rather bulky due to the strange shape (Length is only 13,5 cm with cap, though)
2.) You just HAVE to use this if you consider yourself some kind of geek. Ideal present for a geek.
3.) Diameter used for holding is rather small due to the molds.
4.) If you get used to the molds, you can command it very well. There is a big zone with good grip in the middle of the pen.
5.) The cap is rather small and can't be stuck at the end of the pen (= easy to loose).
6.) Refills are 8,5 cm long and come with their own cap (Tip: If you need a really small ink roller, just use the refills.)
7.) The writing is sometimes uneven in contrast.
Some letters have really very little ink.
It looks very natural, though: Like I've used ink. I fact it IS real ink.
8.) I was surprised at how quick the ink dried: No smearing!

S MOVE ELASTIC = felt tip pen (fine tip) with the outside of a basket ball.
1.) This is a bit bulky as well: 1,8 cm max. diameter of cap is quite a lot. But it's straight over all. So it can go into the pocket.
2.) If you like a basketball exterior... (The material has such a good grip that you might even turn some pocket inside out while taking it out.)
3.) Diameter for holding is big: 1,5 cm (Very good if you have big hands. I get cramps with small diameter pens.)
4.) You can grip this at any side and it writes nicely.
5.) The cap is not very big. It can be stuck at the end of the pen.
6.) The pen can't be refilled. Once empty, thow away 6 Euros (7.50 USD).
7.) Writing at FULL contrast. If you know STABILO 88 pens, this makes more substancial lines.
How to kill a STABILO 88: Apply pressure to the little tip, it is pushed in never to come out again.
The S MOVE ELASTIC little tip has a suspension (=elastic). It retracts if it gets too much pressure - and comes out again.
8.) No smearing!

Result:
The S MOVE ELASTIC is my new favorite.
Looks crappy for me (striped pumpkin with cap), but it is very good to handle.

Google pictures: Try S MOVE EASY and S MOVE ELASTIC

And what about the HIPSTER PDA?
I carefully made a hole in the cap of the S MOVE and connected it to the HIPSTER PDA's front clip (the one you move to the back to open the PDA).
To connect it I used a a cable binder. Maybe a bit of string also does the trick.
Now I always have the best writing instrument with me and it doesn't get lost.
It always returns to it's cap.