I've always been content with Nintendo's styli for the DS family and now the 3DS. They exist, I use them without much thought, and that's about all there is to say, unless I just botched a round of PiCTOBiTS. (In that case, it was totally the stylus' fault. Must've been.)
The folks behind the XStylus Crayon wanted us to give their product a try. After watching the site's mesmerizing transformation .gif far too many times, I figured it was worth a shot.
XStylus Crayon (3DS, DS Lite, DSi, DSi XL)
Given my hand size, I've never longed for a larger stylus -- at least not enough to make a purchase. Those in search of a size upgrade, however, might want to consider the XStylus. It fits in the 3DS (and DS Lite, etc.) as you'd expect, but it can also be widened.
This is accomplished through a quick rotational movement which snaps the top of the stylus in place, causing the sides to puff out slightly. It's a tight enough fit that you don't need to be concerned with unwanted movement during game play, but it's not so tight that it's hard to transform the stylus.
From left to right: XStylus in compact mode, XStylus in wide mode, 3DS stylus, and DS Lite stylus. In terms of form, the shortened XStylus is nearly identical to the unextended 3DS stylus.
There isn't a significant difference in width with the XStylus, although it is certainly noticeable if you do a comparison back to back. Sure, you could go out and get a fattened stylus if you really wanted to, although then you'd have to deal with the awkwardness of it not fitting in your system. A good balance is met here.
It's worth pointing out that the tip of the XStylus reaches out further than it probably should, presumably to allow for easier removal. Visually, this didn't seem like a big deal to me, and more importantly, the 3DS still fits in its charging dock as it should. Be warned, however, if you're one to keep your pencils in perfect alignment.
For the price, you get four styli, and worldwide shipping is included. Neat as the XStylus is, it's still on the expensive side. That said, in my experience, it did everything it set out to do. If you can split the cost among friends, or justify paying $19.99 by yourself, by all means.