When I visited this page, I was confused by the references to two separate products in the same description. The generic OmniPen Pro has plastic tylus tip or ballpoint, laser pointer and LED pen light. With all those functions, it's available in only one form factor.

Apparently Boxwave offers different versions of a ballpoint-pen-or-stylus called the Styra, which is engineered to replace the stylus of specific devices.

If you follow a different navigation tree at the site, you'll see that you can pick a Styra that fits your device. Except that there doesn't seem to be one for either the N810 or the N800.

Boxwave also seems to offer plain old replacement styluses, but again, not for the N810 or N800. The specificity of the ad copy that says it is "precision designed to the exact measurements of the original stylus" must be boilerplate used for all their styluses.

Maybe that's why you can't add the Styra or replacement styluse to your shopping cart from the N810 accessories page.