The maps done by Ordinance Survey are brilliant maps, full of detail and full off information and last for ages. Especally the fully waterproof one's like this which helps keep dry especally if your like me and liable to drop it some where damp. The explorer maps are a nice scale for walking and you are able to pin point your position exactly with it's detail. Only downside with laminated maps if you fold them the wrong way (which you have to do sometimes to see the other side) it does damage evntually. But they are very durable and the best out there.
As for the area. The Brecan Beacons are one of the most breath taking areas in the country. But you proply know that and if you probably plan on going there if you where looking at this map. So simple as, these are the best maps you can find, so walkers, explorers, climbers etc. it's a must. If you buying for driving it may be better getting something bigger because theres maybe to much detail for that, but other than buy it.
If your going around the Breacon Beacons this is a must, so go and enjoy.