We use a Kenmore fridge purchased from Sears probably 5 years ago. It has been working great ever since. As for the freezer, we ended up buying a medical grade mini freezer with much tighter temp control as you mentioned. I bought it through one of our medical supply houses locally. I don't remember the brand off the top of my head. Although, I believe the rep mentioned that a freezer like that was one of those things built by one place, that they have 10 different stickers they can slap on it.
Recently, we did have a scare where a circuit breaker tripped and the team luckily noticed the fridge was warmer than it should be. Of course this could have happened over night and been a large financial loss. I decided that moment to purchased temp data loggers that could alert me of any issues. I purchased 2 of these:
https://www.dataloggerinc.com/product/tr-71wb-wifi-bluetooth-temperature-data-logger/They are slightly larger than an old pager, and can monitor 2 devices at a time. I set them up to report a temp every 30mins and it keeps a log in their cloud service for free. It also has an iPhone app I can watch at and view everything at any moment.
I have one monitoring the vaccine fridge and freezer (2 different probes) and one monitoring a Kenmore freezer provided to us because we are breast milk depot for the Indianapolis Milk Bank.
I was actually really surprised to see the graphs of the temps after setting up. The Kenmore fridge w/ vaccines is pretty solid with very little temp variance (+/- 3 degrees) even set about 42degrees. The medical grade vaccine mini freezer is even more rock solid set at 0 degrees. It varies less than 1 degree.
BUT... the Kenmore breast milk upright freezer varies almost 12 degrees between cycles!! Kind of crazy. It never gets above freezing, but I was really quite surprised to see such a variance. Considering the Fridge doesn't do that.
Anyways, hopefully something was helpful to you in all that.
Nic