It is and isn't - At events lower than national champs yes, providing it's not banned by NoR or SI and at national champs and above no: see the class rules as follows:
In addition to the optional equipment referred to in C.5.1, in a race or series of races which are not world, World Sailing,continental or national championship events, one or more devices may be used in events which (unless prohibited in the NOR or SI) have the capability to measure, display, and record information relating only to the boat’s position, heading, header and lift information, time, and/or speed. Such devices may not indicate to the crew during a race
time or distance to or location in relation to marks, start/finish lines, or other boats.