This is the Uni-ball Signo Gelstick that I brought for sketching in Bali. The model number is UM-170.
It's a simple non-eye catching design. It's made of plastic throughout. I like the lightweight feel because it makes me feel like I'm using a pencil. The grip has a triangular groove which makes it a bit nicer to grip but for long using sessions a rubber grip might be better, but it's a non-issue really.
The picture above shows my used up pen.
The stainless steel tip is roller ball and it's 0.7 so it produces a 0.5mm line.
Ink is fade-proof and water-proof. I can only speak for the black colour, but the pen also comes with 7 other colours. The black is dark, not pure black but very close which is good enough for me. There's no bleeding, feathering as that is the advantage of gel ink.
The ink is pigmented so it doesn't break down when sprayed with fixative.
It writes and draws very smoothly. Ink flow is great until the point when it's almost empty and that's where it starts to skip a bit. So it's good to have an extra pen while out drawing.
It dries fairly quick so you can use watercolour or other medium over it.
The best part about using this pen for drawing is it does not create a blob at the end of the line unlike other roller ball point pens. That's even after drawing a very long line. It's a major plus because each line you draw will come out in the way you want it.
You can click the above picture for a larger view to see just how consistent the line width is.
Another big plus is how economic this pen is, and you can get it in a 12-pack box for even more savings.
Most highly recommended. Really value for money.