My thoughts, and many others, self defrosting units will cause freezer burn
more than manual defrost. Temperature fluctuations help cause freezer burn.
I don't have any full size units right now. I've data logged typical upper
freezer refrigerators. During defrost air temperature can go well into the
20s. If it's opened during that period, even worse. I was just reading
searches, because I never really worried about it much.
I bought my parents a large sears chest, around 1970. It sat in the garage
for 35 years, always running. I ended up giving it away still working. It
got close to 32 degrees at times in the garage. It was not used that well,
mostly empty. Great for large items, and making ice bricks.
I found a problem recently. A self defrosting unit, against a cold wall
will condense water vapor, causing mold.
Greg