I think the Nikon Omega is the one specifically for muzzle loaders.
That being said, I have no experience with the Prostaff that was just released, but I have used the one that's been out for the past few years. The ones that Cabelas has on sale. It' was a decent scope, but it didn't really excel in any specific category. I'd use one on my muzzle loader without hesitation.
At the $160 they normally sold for, I'd not recommend them as there are so many better scopes in that price range, but for the $95-100 Cabelas had them for, they are about the best you can get in that price range. I found the lowlight performance to be worse than I'd have liked, but it decent enough. The glass was really just not great. It was nearly identical in most all lighting conditions to the cheaper $30 Simmons Blazer I was replacing it with. I soon found out that if shooting in the snow that I saw a lot of chromatic aberration with it. This kind of turned me off from it, as even with the Simmons I didn't see this in similar conditions. However, the glass was still plenty decent enough for hunting.
The other complaint I had with it was the turrets. They required a coin or screwdriver to adjust. This isn't a big deal if you set it, and forget about it, but if you are like me and like to adjust them fairly often these things are kind of a pain. Not a major deal killer though.
Now that I've gotten past the bad, the good about this scope is it seems really durable. I wasn't super rough on mine, but I wasn't all that easy on it either and it never lost zero. For the hunting season I used mine it held up perfectly. So it seems to be a solid durable scope if you don't need great glass and great turrets.
I've since upgraded to a Monarch from the Prostaff, and honestly I was a little disappointed in the glass on it too. I honestly don't see much of a difference between it and the Prostaff glass wise other than the chromatic aberration isn't quite as bad, but the glass differences are very very small. However, the tracking is spot on with the Monarch, and it has pretty good turrets. Overall, I feel the Monarch is a better scope, but just comparing the glass, it's not much different.
The Burris Fullfield II's I have, blow both the Monarch and Prostaff away in the glass department, and for the normal price of a Prostaff, I'd highly recommend looking at the Burris, or one of Vortex's offerings. If you are getting the Prostaff on sale though, like I said, it's a great buy for $95-100, and I wouldn't hesitate to use it hunting.
This is an older writeup, but worth a read.
http://opticstalk.com/inexpensive-sc...opic21176.html
It pretty much mirrors my experience exactly.