Pickles,
Nationally the Opposite Lock franchises are pretty good. They stock the products that Dolium import from South Africa which are pretty much all approved by Land Rover South Africa as they install Front Runner products pre-delivery. Quite a bit of the LR brochure OME kit is deemed unsuitable for conditions outside Europe, hence the advice on your first post.
Obviously Mulgo Expedition centre sells the same and installs to a very high standard for those close enough to make it viable. Daniel the owner is a avid Defender fan and by all means a specialist on his product.
ARB sells some good products, but they are not by any means Land Rover specialists and the quality of workmanship can vary from branch to branch (although we've not read any complaints from people with their bull bar installed).
Landybitz (Juddy on here) sells some really good gear and can by all standards be called a Land Rover specialist installer as well and are recommended if geographically viable.
I've only mentioned a couple that came straight to mind and my apologies to any vendors on here that didn't get mentioned!
Here in Perth we've got some really good independent specialists that would rival any, so if you post on your area specific sub group you'll have all the answers!
Stay on the forum and you'll learn an immeasurable amount about our very unique vehicles.
Cheers,
Lou

