Did this last year. Neither hilly nor really off road. The bulk of this race is on road or tarmac (cycle) paths. The long haul above Talybont Res and through the forest is a slow very gradual climb, only steep in the very last section just before it reaches the road and the highest point of the course. From there it is more or less constantly downhill, taking road options. Road shoes would suit.
You'll be able to complete this in almost the same time as a road 50-miler. Good coach service from Sophia Gardens (free parking) and comfortable start HQ at Brecon.
The urban bits, especially Pontypridd, would be hard to follow but last year at least ROs put yellow arrows on the ground for us to follow. Suggest if you can recce the bits through Merthyr and Pontypridd. Don't take the high route past Castell Coch, unless of course you like hills!