Whats the catch with debt consolidation companies?

[Will C.]

So I keep getting these debt consolidation letters in the mail and usually I just toss them not giving a second thought. I decided to open one today just out of curiosity. Are these companies legit or is there some fine print catch going on here? On the surface it looks like a no brainier, trade high interest debt for lower interest debt, save thousands on interest. Just wondering if this could be a short term solution to lower monthly payments until I ELOC equity from my last renovation to pay back high interest debt. Thanks