It depends on the CDOs and how they are constructed and what contractual protections you have. The good ones aren't bad at all. The bad ones only work if you stick to the shift. If you think you're going home and running around with the kids and "getting 'er dunn" around the house or side business with maybe a nap, you will be in a world of hurt. Ditto for a schedule with a lot of red eyes as well as many of the lower end international trips.
There are plenty of safety critical third shift jobs in society. You have to adjust yourself to do them though, or they are incredibly unsafe. My problems with the CDO's as we agreed to them at the time were the block time length (too long), inadequate IROP min ground times and the fact that they were sprinkles into the bid packet and would end up on people's "regular" lines as well as sprinkled among reserves. The reserve part is of course inevitable, but there needed to be downline protections, such as nothing until 10AM (day one reserve standard) the day after you land.
Our TA CDO's and FAR117 had some good stuff in them, but they were both jacked up with concessions to the company to mitigate the cost side.