I've been using the power bars, in particular I like Pria bars, and so far, so good. For breakfast, they work really well because they keep me full until lunch. This is even true after my morning walk, which is amazing because I'm usually starving since it's about 100 degrees outside right now.
Yesterday, I had one in the morning for breakfast and it really kept me until a 1pm lunch. Then I had one around 5 or so (along with some grapes), and that gave me enough energy to go for a walk in the evening (since I couldn't take one that morning).
A few things to keep in mind, though, for anyone thinking of giving these a try. First, make sure you drink a lot of water or similar liquids. I eat one for breakfast and drink a small pot of black tea with it and then also at least a large glass of water after that. This helps keep you full also and from having any possible stomache problems, which leads me to the next issue with these guys, bathroom time, and a fair amount of it. And, I don't just mean a number 1, if you know what I mean. This is also one reason I try not to eat one after 5pm.
I prefer the Pria because they taste good, but they also have fewer calories than most of the other protein bars I've found. Of course, there's a trade off because they also have less protein (5g) than these bars too. If I were a body builder, this might be more of an issue for me. But, I'm using these for weight loss (hopefully), and I'm also interested in addng more protein to my diet because I don't eat much meat.