Hi Craig, Croeso! (Welcome!)
I've not heard of the garage you suggested so can't help there I'm afraid.
Not yet had chance to check out the Cardiff dealership personally so no use there either sorry.
The only place I can suggest due to fellow forum members comments is, as Richard has said, Dick Lovett's Swindon.
I searched for a recommended Independent specialist when I first got my car and couldn't find one inside 100miles. There is however, a comprehensive list of Dealers and Independents on the forum which is compiled on recommendations only so you should be well served with any of those. If you do come across one not on the list and can recommend them on experience, please do add them to the list as we are not yet spoilt for choice in Wales and the surrounding areas.
On the plus side, if you do have to travel to Swindon then at least the drive over the A470 will be fun.
All the best,
Ru.