The Brandenburgs were an improvement over existing German battleships when launched in 1893. They were useful supporting the coast defense ships and were a technology stepping-stone to further pre-dreadnoughts designs. While these designs were not used actively in The Great War they were important as training and defense ships in the years leading up to the war. If needed, they could have been of some use in the Baltic in 1915.
They, and the Kaiser Friedrich III class, are to play a crucial part in a book I am working on dealing with a naval war in an alternate time line. For now all I can say is it is a naval heavy book dealing with the politics and technology at the turn of the twentieth century.
The Brandenburgs with all of their limitations came with a punch, six 28cm guns and fifteen quick fire guns. The have the ability to cause damage to both heavy warships and torpedo carrying craft. I do look forward to seeing them on the table.