If you want the smoothest action, and highest flick ability and fidgetability, I'd recommend you pick up a Para 3 in G-10, or maybe a Domino. They really are quite nice to play with, and they cut pretty darn well too.
Tha Native 5 has a couple of things "going against it":
- Lockbacks take awhile to break in, especially the lightweights.
- No thumb ramp, or "Spyder hump" means you don't get the same kind of leverage to fling the blade open.
- Lockbacks are very secure, and easy to operate.
- No thumb ramp, or "Spyder hump" means it's very compact in the pocket.
- Tremendous cutting power in a very compact, lightweight design.
- Great ergonomics
- Made in the USA
It can be difficult to describe a knife's "action" over the internet. I'll echo the other commenters here that if you got the knife from eBay and it is really truly painful to operate, you may have a counterfeit, a factory second, or an otherwise-used model. No Spyderco should really be painful to operate, although if you're cycling the knife open + closed hundreds of times in a sitting you're likely going to develop some hot spots.
If the grittiness really is like a grinding of metal, that's probably what you're doing. Counterfeit or not, you'll probably want to take the knife apart and clean it out. Go slow, use good torx drivers, a little lube on the pivot, and a little blue lactite on the screws.
When in doubt, send it in to Spyderco and they'll fix it up for a nominal fee (or identify it as counterfeit). if it is counterfeit, eBay has pretty good buyer protection.