Rode these over 3000 miles so far and have had only one flats big, nasty thorn. Same tires as before, same conditions as before, all surfaces. These tubes made the difference. They may be a little thicker and little heavier, but doggone, they work great. I get the 60mm smooth for my carbon 50s.
I'm not aware of any reputable objective report that shows that one brand of butyl tube is better than others, so I don't see the need to pay more. Mine have worked fine as tubes go (including the ones with the name Kenda printed on the tube but with a different name on the box), which is to say, they will puncture when pierced by sharp objects, like all tubes.
I discovered this brand years ago when I found them reboxed at a bike shop. I have been purchasing Kenda tubes ever since. They are extremely consistent on the amount of air they lose over time. They have never let me down.