It is hard to call low-cost gear overrated, IMO. Nevertheless, there are a couple of names that come to mind here: ASI cables and Grover Huffman cables. Too much hoopla for too little performance.
It is easier to call high-priced gear overrated. A number of items come to mind here: the EMM CDSA SE CD player was a $11,500 total dud. IMO, it simply rode on the wake of the name Ed Meitner. Gabriel Gold cables were a total dud. Some of their prices have since come down to visit us on planet Earth. The AMR DP-777 blew up twice. They had design problems but instead of disclosing this to customers they decided to cover up the fact.
The Berkeley 1 DAC. Never mind what the revered Robert Hartley has to say. I have the feeling he may just be cutting and pasting to save writing time. Like Ted Denney for his Synergistic Research Tesla series cables -- and many other products including the famous Cells. In any case, he needs to start using spell check. He continues to write then in place of than. And he needs to use "increase font size" on his site that continues to use font size 4 -- maybe to prevent folks from reading the fine print.