My sharpen experience isn't good.
First off, crit itself is limiting. This talent doesn't increase crit damage, it only increases crit chance.
Second off, ACC, while nice, isn't something that is all that important for most players. It comes in handy if you are head to heading max dodge heroes, but that isn't common by any means.
I am going to say, the vast majority of players, have virtually no additional ACC on any of their heroes, and don't really need it.
Conclusion: Crap. It's especially bad if left at 5/8. Sharpen might have a place, and it can be effective under certain situations, but those situations are not what I would consider common.