With my first daughter, I had tried a different brand. After the first day in the diaper bag, I had 4 feedings worth of formula all over EVERYTHING in the bag because it didn't seal tightly. I went with the 4-oz travel "tubes" of formula, which aren't exactly cost-effective unless your baby is eating 4 oz or 8 oz at a time.
Right before my second daughter was born, my mom found several gently-used baby items at a garage sale, one of which was this dispenser. I was skeptical after my experience with the other dispenser, but after trying to take the whole lid off I realized just how hard it was to open. This is a good thing! It keeps it from spilling in my bag and keeps my toddler from opening it. The spout cap is easier to open than the whole lid, but is still snug enough to stay closed. If you try to take the whole lid off while there's powder in it, you do have to be careful, but I don't find myself doing that a lot. Usually, I open it when it's empty, fill it up, and use what's in it before I open it again. I haven't had any issues with powder leaking over into other compartments, but I've always twisted it to the middle of each compartment. If you look at how it's made, the lid/spout is curved, so if you don't get it mostly centered, yes it's going to spill over. However, because of the tight fit, if you center it, it doesn't move/twist from movement in the diaper bag. The seal is worth the split second of effort, imho.
I have been using mine for 2 months now (and that's after getting it secondhand) and it's worked great for me. With daycare and overnight trips to grandma's house in the near future, I will be buying a couple more of these.