I have a round Presto unit similar to American Harvest or Nesco.
Wife got it for free (for me) as an anniversary gift from her former employment.
I don't use it a lot. I only need to dehydrate peppers every 2-3 years.
I naturally air dry my herbs.
If I dry herbs in the Presto, the fan tends to blow them around and shatter the leaves.
I tried drying tomatoes, but found I prefer them smoked and oil packed.
If I was buying a unit to use a lot, I would avoid the round stackers.
The rack style are great, but really think about how much you plan to use it before dropping a lot of coin.
I lost the romance pretty fast.