Have ridden this route last weekend West to East. I would advise others however to ride it East to West if you are newbie, unless you really like challenge.

It starts gently from Britton Ferry canal, for miles its flat, very unusual for Wales to be flat :) Until you get to Myrthyr, then climbing start. 

There are 3 bigger climbs in total I  think.  Ridding it from the East would be easier as hard part it at the start, rest is just down towards the coast. Overall route is 80% traffic free. There are roadworks in Myrthyr (at the time if this writing) which force you for a detour.  Watch out the gates, there are far to many of them. I had to jump at least 10-15 of them on the entire route, travel light. I've done in a day on the gravel bike. Enjoy some of the nice scenery South Wales has to offer.