I have been using many versions of these over the years. Sure, they are cheap, you can put packbait inside, it holds, and you can catch carp. The rate of hooking with these running rig feeders is however inferior comparing to fixed weighted method feeders. Often the carp even spit out your hook without you noticing that there was a bite or you see it as tiny bite. Good video to watch is NashBait evolution of terminal tackle.

Bought these and other spring feeders from another site and these are far superior. Bait inside feeder has stayed intact so far which adds to the bolt effect. Really awesome product!

It holds pack baits unusually longer time and allows long casting. I used it as inline feeder. An must have item in the tackle box

I used the unweighted small and large feeders with various packbaits/groundbaits and I must say they held very nicely even on longer casts. Works best when used as an inline, running rig. The unweighted feeders work very well when fishing still waters and will hold your line in place on the bottom.