Hi Steve
I think the TDA is a good idea and generally does a good job. My problem is the fees, I have enquired a couple of times over the years and always been surprised by how much it costs to become a member. Its OK for major suppliers or organizations that can afford the cost, but small independent installers have enough overheads as it is. If membership was made a legal requirement it would be fair for all as we would all be operating with the same overheads but until then I will be opting out, unless you  reduce your fees in the new year, worth a try.