Originally posted by KentoHuh?
Sure, it's written by Toyotaro, but it stops with Final Form Freeza against base Goku. It's not even a full story arc more just a story to provide hype for the movie without spoiling the ending. So it's canonicity is very dubious at best. It's half a manga if so, and its not included in the volume 1 or 2 of the series either.
The RoF manga literally carries the exact same canonical affiliations as the DBS manga. Same author/illustrator, same overseer, same serializing media, same publisher, etc.
The story stopping just before Freeza becomes Golden certainly doesn't make it non-canon, and/or 'dubious' material. Remember, the RoF manga was actually released just BEFORE the film -- they didn't want to spoil the film's 'big reveals' by depicting Golden Freeza and SSB Goku(both transformations were completely unknown at the time.)
But again, there is absolutely NO reason to doubt its canonicity.