I’ve read The Golden Bough. I’d exercise the same caution with it as I would with The White Goddess. Frazer’s work is not really considered to be that great for comparative religion and many of his ideas have long been discarded by anthropologists and ethnologists alike.
George Watson MacGregor Reid was a bit of a mysterious figure. He was the chief of The British Circle of the Universal Bond, which still exists today as the The Druid Order (An Druidh Uileach Braithreachas). They have a website and there’s some information online too.