Does the Nesco FD-37 have a temperature control?

No. It has only an on/off switch, and the heating element runs at a fixed high temperature, around 160°F. That is fine for jerky and fruit leather but too hot for delicate herbs.

How many trays does it come with, and can I add more?

It ships with four trays. Nesco sells add-on trays for its round units, and the FD-37 can take extra trays up to the height the base and fan will support.

Is it good for making jerky?

Yes, jerky is what most owners use it for. The fixed heat is in the right range for meat, though you should rotate trays and check doneness since there is no timer.

Can I dry herbs in it?

Only with care. The fixed heat can cook and brown delicate herbs rather than dry them; keep trays thin and check often, or choose a model with a lower thermostat setting.

Are the trays dishwasher safe?

Yes. The trays and base are dishwasher safe; the fan and heater unit on top should be wiped clean, not washed.

How does it compare with a square cabinet dehydrator?

A square cabinet holds more, usually has a thermostat and timer, and dries more evenly. The FD-37 is smaller, simpler and better as a low-cost starter unit.