Have ridden both rabbits and cycos routes. Cycos I did from Tywyn up.
Enjoyed both very much.
Yes a great route(I live on it)but try..a right to tal-y-llyn onto Tywyn then A493 thru Aberdovey back to Machynlleth A487 and back to Dolgellau.You get some great 'coastal scenery', stop on Tywyn sea front for a coffee and burger/icecream. Lovely twistys as well.
A nice A road which starts off simple at the Dolgellau end and becomes very twisty as it nears Machynlleth. Really tight in places so you need to be quite focused