I agree with this.
It takes longer to build a good forensic practice than a good private practice, and the work is unpredictable. You get a nice wage. It's not hard to get $300-$600/hour, with criminal cases on the lower end of the scale and civil work on the higher end.
But this is almost impossible to pull off full-time. Aside from the scheduling issues, you get good pay by doing good work and the WORST forensic psychiatrists are those who don't maintain clinical skills. Their work is shoddy and they tend to be bottom feeders, which is great for a quick buck but they typically find it harder to get decent (i.e. higher paying and higher hours) cases due to reputation. The best way to make a decent living in forensics is to maintain a paid faculty appointment, but it's tough finding one that is compatible with taking frequent time off to meet with lawyers and testify in court.
Regarding getting time off, most employers I've talked to indicated that any time away is vacation time. The only time I testify in court without taking the day off (or comp time) is if I'm subpoena'd as a fact witness, NOT for my forensic practice. And if you get a faculty appointment, many places will charge you a 15-25% fee for any forensic work you do on your off hours (although in these cases, they'll also often help with billing, office space, and malpractice). And some places will have you sign a contract forbidding that you do forensic work on your off hours (I'm looking at you, Kaiser).
I definitely make a higher hourly rate as a private forensic psychiatrist than I could make in any other area of psych. But I definitely can't multiply my hourly rate by 40 and call myself done.