I have both and for me they were simply a pointing device ie I havent made use of the degree reticules for navigating with star charts.
The main difference is in the size and weight. The smaller rigel comes with two mounting feet designed to fit different diameter OTA tubes and can easily serve double duty if you own a refractor as well. You wouldn't put a telrad on a small scope like a refractor.
The Rigel works just fine on my 10" dob
