Although it is recommended to always use the latest stable firmware for the equipment, the fireTEK equipment will create mesh networks and communicate across different firmware versions allowing you to fire your show.
Obviously, certain firmware version-specific functions will not be operational.
Also, firmware updates are conducted via computer and a USB cable - there are no additional update devices to purchase.
Links to Firmware Notes:
The following video from Team fireTEK USA shows how to update FW for the current FTM Controller and FTH modules