I'm going to invest in a food dryer. Any important criteria/really reliable makes?

I know that Carol Deppe in her book The Resilient Gardener goes into detail about what to look for in a food dehydrator. You might want to check out the information that she provides.

Get the largest Excaliber food dehydrator that you can. They are pricey, but the others have a circular design which wastes space in the middle and prevents you from tinkering with the different trays without taking all layers apart during the drying process. If you go with one that has less trays, you will wish you had gotten the one that holds more, cause it performs JUST THAT GOOD. Fruit roll ups, jerky, banana chips, kale chips, dehydrated ingredients and soups for camping, dried berries... You'll always have the thing going, especially in the harvest months. It's unbeatable.

I have had several American Harvest dehydrators. They are adequate but it takes a very long time to dry product, especially fruit. Last year I invested in an Excalibur Brand dehydrator. Because of a better fan and the ability to remove racks you get better airflow and faster drying. This was great for large grapes. Check out their videos on their website. The square design is more efficient and holds more. Drying sheets are available for fruit rolls. I have not used these yet.