Yes. I've sued four collection agencies and got settlement checks from three. The last one I just kind of let go and the court dismissed it (without prejudice). In the three cases, the settlement also required that they completely remove the account from my credit reports.
So yeah, it works great. Nobody can argue with the math. They are going to pay their attorney $200 per hour to deal with it. So if you figure answering the original petition and maybe one set of interrogatories, they're out $600 and we've only gotten started. Then they have the downside of acutally losing - that's potentially another $1000 and who knows what in attorney's fees.
My downside? Nothing. Nada. If I lose I don't have to pay their attorney's fees. I don't have any of my own because I do it myself. What if they countersue? Generally they can't. They don't have standing to countersue - I don't owe them the money, I (allegedly) owe their client the money.
Bait, document, bait, document, sue and settle. Not one got anywhere close to seeing the inside of the courtroom.