The version of dehydrator I use is American Harvest by Nesco.  It is a round unit (about 16-18 inches in diameter) and typically comes with 3 trays--one having a solid plastic insert for items that are mostly liquid when you start.  The unit has a dial on top to control the heat level and there is an index printed on the top to give you temperature settings for a variety of items.

I added a few extra trays to process more items at the same time and bought extra plastic inserts.  The only deficiency I've found on this unit (if there is one) is that it doesn't have a timer.  I guess I could always plug it into a timer if I felt it was necessary.

dd