I am not clear as to when your brakes are slow to release and squeal.
Having spring brakes that are slow to release is not uncommon, particularly if you live in an area of high humidity or lots of rain. It doesn't take much to get the brake lining to get stuck with rust onto the drums.
Even when the brakes are not rusted onto the drums it takes a few counts before the spring brakes release completely--between a 5-count and a 10-count is not unusual.
If your spring brakes release within the 10-count I wouldn't worry about them. I would be more concerned about what pressure the spring brakes apply automatically--too high and you won't get enough warning to get out of the traveled lane of travel and too low and you will have no service brakes left at all.
When the drums are rusty the brakes will grab and squeal quite a bit until they are all shined up again.
Some brake linings actually squeal louder and longer than some others.
I remember one set of linings I had on a bus that if I applied just the right amount of pedal pressure I could get the brakes to squeal all the way down the hill. Just a little more or a little less pedal pressure and no squeal. If the neighbors on the downgrade weren't awake before I headed down the hill I doubt they were after.