I started with a 510, and the main problem is that the batteries don't last long. Especially if your a heavy user. You would get 2-3 hours max out of a 510 with heavy use. The Ego lasts me all day without a recharge. As for the size of the ego, it's no worse than a large fountain pen. It's actually smaller than some fountain pens I've seen. I have no experience with the volt, so I can't comment on it.