I made my own but, for sanitation reasons, decided to cool a water bath on the outside of the beer rather than stick a cooling rod into the beer itself. The principle is similar, though, and I have learned that the key to good performance is
lots of insulation. The less heat that leaks in from ambient the better it will work. Their insulation bag is not good enough. You need a couple of inches of the best foam insulation you can get: start with a picnic cooler with your vessel inside it, and make an insulated top that has a hole just large enough for the top of the apparatus to stick out. If the hole is larger, fill any cracks or gaps with weather stripping or cover with blankets. If you want to cold crash you can put ice water into the cooler to boost the cooling capacity. I use the same cooling module as the Brewjacket and can achieve 34 F with help from some ice, provided the ambient temperature is not above 80 F or so. A thermoelectric module is a very nice, compact and quiet solution for cooling beer and regulating the temperature very tightly, but not as powerful as a refrigerator.
Here is a picture. If you use the brewjacket you won't need all the stuff to the left of the cooler. I usually wrap blankets around the top, but removed them for the photo. If you make a setup like this for the brewjacket you should be able to lager and cold crash with only minor interventions to add ice.
https://drive.google.com/file/d/15fH7MYDjJxmJQ2xPySBVRPTJK9l_gisE/view?usp=sharing