My XWH took one. After so much TT, and me contacting the OW only to be told by her that there was an additional OW, I wouldn't allow him back in the house without one scheduled.
We found one in the phone book. He was an ex cop, used to do them for his department. The cost was steep. I think somewhere around $350. But when he saw we were parents of three and I was pregnant, he cut us a break.
He helped us form I think it was seven questions that could be answered with a yes or no. I gave my XWH one last chance to say anything else, and the cop also stressed that the test would detect his lies. He fessed up to one last minor thing, took the test, and passed it.
I left feeling such relief. I knew there was a chance he was still lying and the test was false...but I decided it was the closest I could get to the truth. I needed that peace, and it's what finally helped me move forward.
The marriage didn't last. We D. But I will never regret the money spent.