I have a few other TwoSun Pens, and the PEN53 is the best BOLT action one by far. This one is robust, and has a little larger barrel, which I appreciate. It's built like a tank. Reminds me of something medieval. The others seem too light, but they are nice too. My other favorite TwoSun PEN is the PEN01 (not sure if that means it's their original TwoSun Pen or not). That one has a screw cap, that can be moved to either end, providing balance (and of course, something to fidget with).

All of these pens take the standard Parker Pen refills, which you can find somewhere on the webs.