Not a lawyer
The PI provided video evidence and a factual report giving details of each encounter. The cost was high because of the amount of time and effort it took to collect the evidence at $70 per hour. Sometimes, they needed 2 PIs on duty depending on the situation, which doubled the cost per hour. After getting the evidence, had my case
gone to court, the PI would have acted as a witness in the trial (for a fee). PIs are licensed, so they are considered to be independent, credible sources of information. Most divorce lawyers work with specific PIs they would recommend, so if you’re interested in going this route, speak with a lawyer to get their recommendation for your area.
Regarding child custody, if the paramour is a negative influence on your children, then it can impact custody. For that to happen, the children have to be exposed to the paramour and the paramour has to be a pretty bad person (drugs, amoral activities, etc). Otherwise, the act of an affair in and of itself will most likely not have a bearing on custody.
Regarding alimony, you are correct that an affair can impact alimony in your favor if your spouse is the dependend spouse. If your spouse is the dependent spouse, alimony is wiped off the table. If you, however, are the dependent spouse, alimony will not be increased because of the affair. I made the assumption in my last post that you are the dependent spouse when I said it wouldn’t be impacted, so if I assumed incorrectly, I apologize. In my case, my cheating spouse was the dependent spouse. It was cheaper for me to pay $10,000 for a PI than it would have been to pay alimony and I wanted a near guarantee with solid evidence that I wouldn’t have to pay alimony.