I feel the best way to evaluate snack replacement and meal replacement bars is by evaluating their macro-nutrient breakdown. If they're mostly sugar, then you might as well eat a Snickers (and indeed, there's something called Snickers Marathon which is objectively BETTER than most of the "nutrition bars" out there). On the other hand, if they have lots of protein, then you're actually getting something different than just another candy bar. So the easiest way to tell is to divide calories by protein grams. The lower the number, the better the bar.
Considering the Low-carb Pria's are supposed to be low-carb, they don't stack up well against other high quality bars:
Regular Pria's are 22 calories per gram of protein.
Luna Bars are 18 calories per gram of protein.
Low-carb Pria's are 17 calories per gram of protein.
Zone Perfect bars are 15 calories per gram of protein.
Balance Gold bars are 14 calories per gram of protein.