I purchased one of the Flyweight Designs FlytePacker and have taken it out a couple times on standing and moving (albeit slow) water. Here are a couple of things I noticed:
1)Deflated it is extremely light and packable. I would say it is approximately the size of a small loaf of bread. This is crucial to me as I primarily bought it to use in an adventure race.
2)You are not going to win any races against a kayak or canoe, but that should be obvious. With a kayak paddle on my first voyage I was able to average around 2.5 mph.
3)It is much more stable than I anticipated. I was able to actually stand up in it when I was on flat water.
4)I had plenty of room to move around when paddling by myself, and was able to paddle both from a kneeling position up front and also by sitting back with my legs extended, crossed, or knees up. There is enough room for two people, which is possibly how we will use it during one of our races.
5)The raft seems very durable, although I haven't tested this too far. I would stay away from sharp rocks or running into sharp sticks at high speed, but thats kind of my policy in any watercraft.
Overall, the raft is perfect for how I am planning to use it. I am going to try to glue some additional lash-tabs on it (it comes with three built-in), but other than that plan no other alterations. I'll admit, I originally was looking into trying to make a pack raft myself, but after reading some other posts, this seemed like a much easier (and quicker) way to go.