Hi Alan.
I've done the half twice and I did the marathon last year. The course route and profile are on my Garmin trace here:
https://connect.garmin.com/activity/541709132For the most part it's undulating but there are some killer hills. Because I knew the course, I had an intentional strategy of walking up the steepest of them. I got a few odd looks to be walking at only 3 miles but I wasn't moving much more slowly than people 'running' and I caught and passed anyone that passed me quite easily as they were blowing from having run while I was fresh.
The hill at 3 miles is quite a lot steeper than Penylan hill (on winter 10) and a bit longer. More like the steepest bit of the road up to the Black Cock or even the Wenault.
The short sharp one just before 6 miles is deceptively steep but over very quickly.
The hill at 15 miles isn't too bad as you're well rested from the long downhill and flat section before it. It's actually not too steep either but goes on a long way.
The road up through Manorbier around 20 miles is tough. Probably only similar to Penylan hill but your legs have just taken a bit of a battering flying down to beach level.
Similarly, the next one at 21.5 seems to go on for a long time and there's a mean little kicker near the top after a false summit.
After that, it's undulating again before you fly down the same hill up which you came at three miles. Very steep and very hard on the legs.
Nice easy flat section to recover before the last drag up the final hill into town. That's shortish and sharp but it depends what you have left in your legs.
A tough course although, no doubt, not a patch on Snowdonia. It's a very well organised and very friendly race. Due to the route, there are some sparsely supported sections but the scenery is stunning and where you pass through villages, the locals are out to offer encouragement, drinks, sweets etc. When it's been roasting hot, there have also been garden hoses and sprinklers that you can take advantage of. Since the half starts in Pembroke at the halfway point of the marathon, there's great support there too. Especially if you can get there around the time that the runners in the half are getting ready to set off. Since the marathon is the culmination of the Long Course Weekend, Tenby is buzzing all weekend and the locals really get behind the event to support it.
In terms of training, I'd advise lots of trips to the Black Cock or Caerphilly mountain. Similar profiles and similar roads. On the day itself, be aware that it can get very hot. The second time I did the half it was 30C and there's not much shelter out on the route so hydration is massively important. You might also want to get used to running in a hat.
That's probably enough waffle for now but if you want any more info or I've missed anything obvious then feel free to ask.
Steve