Mine will shift around, like the air temp in the fridge will move maybe 10 degrees between what it is set to cool to, and when it's set to come on. But that's fine, it's nowhere near long enough to cause any amount of liquid to warm up.
I fermented a batch in there a few weeks ago and the temp was stable for the entire fermentation.
The freezer thing, mine has that too, if you mean it's a normal house-type full freezer on top with it's own door thing. How mine works is the freezer will only actually stay at freezer temps when the fridge is less than 55 or so. At 60-65 in the fridge, the freezer will be NEAR freezing, and maybe sometimes into freezing, but my icepacks in there are all sorta squishy.
Not something I'd leave meat in, for instance...but good enough for hops, ice packs, etc.
The freezer fans just steal the cold air when the fridge compressor kicks in, and the fridge part of mine takes precedence of the fan over the freezer.