I don’t have extensive experience with Rega, but I had an RB 300 and an RB 900 or 9 arm (don’t remember the exact naming). There were two points I didn’t like. The inability to adjust azimuth and a quite „small“ sound in terms of frequency range coverage.
But I never had a complete Rega setup, where things might come out differently. At the time I heard it, Rega was entry level. The bigger arms had better tolerances with certain audible advantages, but otherwise played in no really different league imo. I know there are other opinions.