Its been my learning that Flatheads mainly go for live bait...so this question doesn't appky to them. I think it might be geared more towards Blues and Channel cats.

So Walmart clearance had some Magic Bait Brand Big Squeeze Shad flavored paste in a tube for $1.50 a tube. I cleaned em out just because and got 4 tubes.

Is this stuff any good? Or did I just waste my money?

It will more than likely catch some channels, they'll eat about anything. Blues,especially large ones, tend to be fish eaters. Big channels also tend to be fish eaters more than anyting, they don't grow large scavenging stuff off the bottom. If you're just looking for some eater size catfish though I'm sure you'll be fine with it. If you're looking for bigger blues or channels I'd suggest the real thing, either live or cut bait. 

I haven't gone Catfishing in years. The lake I fish was all fished out of cats years ago. Last year they reintroduced Channels. Late April this year they put 1500 lbs of Channels back into the lake. Saw one a week ago that wouldve gone 5lbs+ easy.

I actually used that stuff years ago. A friend and i would put the paste in these pladtic tear drop shaped catfiah rig with small holes in it with a treble hook attached around the plastic. We just filled it up with paste amd caught toms of channel cats. Blue cats though you are better off using large cur bait either drifting it on a 3 way or near bottom.

never used the stuff myself. i assumed its just like their dead shad packages, useless. when i want to catfish i just pick up some nightcrawlers, chicken livers, shrimps or use cut bait...

I've found that (like everyone else said) channels will hit on anything.  Have a lot of luck with frozen shrimp with them.

 

I really never catch Blue Cats on anything other than fish caught on the same body of water I am fishing.  Typically I will catch some sunfish, cut them in three's (tail, mid-section, head, toss the tail) and fish a combination of mid-section and head to see what they want on that day.  

 

The only store bought baits I've heard has a lot of luck is goldfish.

 

And to share a secret (cuz really, I don't care...or I was duped)....I fish the lake where the world record was caught two years ago.  The bait that he supposedly caught the fish on was chicken breast, soaked in RED kool-aid with garlic powder.  I have used this bait and caught fish, but cannot verify whether or not this was the actual bait used for the world record.