Thank you for this discussion. I hope the Community finds it useful.
The risk associated with the described technique is not so much in the cooking, but in the nature of the product and the phased cooking process used. The risk is it might make you and those you serve very sick.
The risk is in the spores produced by harmful poultry bacteria which may become active bacteria while your food's temperature is in what is commonly referred to as the Danger Zone, 40F to 140F. Our challenge as cooks is to minimize the length of time food spends within that temperature range. Using a technique that puts the food in the Danger Zone longer and more often than necessary is a risk taken. To keep bacteria at a safe level i use a cumulative maximum total time of 4 hours in the Danger Zone. That's from the time the raw product leaves refrigeration until the cooked product is served. That's a generally accepted foodservice industry standard and what most public health inspectors are taught.
An example of prolonging the length of time in the Danger Zone is frequently incomplete chilling. Using a 50% ice bath hastens cooling and should always be used to rapidly and completely cool your food. We know an ice bath requires about 3 hours to chill cooked food to 5C or 41F to a depth of 3 inches. (Baldwin 2008, Table 1.1) A wrapped turkey swimming for 30 minutes in water won't do it. Heat transfers to ice water a lot faster than it will to the static air in a refrigerator. The packaged turkey's interior likely spent much of the night in the danger zone. That's a risk.
If someone is going to cook any large piece of meat or poultry it's safer to do it in a single step and be aware of the internal temperature attained. Doing that reduces the risky time food spends in the danger zone during the cooking phase, then during the cool-down and refrigerated phase, and again during the reheating or rest of the cooking phase, and then up to service time.
The improper handling and chilling of leftovers presents yet another risk.
P.S. Nathan Myhryvold, former Chief Technology Officer at Microsoft and the author of Modernist Cuisine wrote the following about the difference between chilling food in an ice bath and in a refrigerator:
" . . . heat transfer from air to a solid, via natural convection, is quite slow. It is about 100X less effective than stirred water.
Natural convection in air (i.e. not forced with a fan) will transfer about 20 watts per square meter, per degree C of temperature difference.
A stirred water bath will transfer about 2000 watts per square meter per degree C of temperature difference"