I agree, if the Chaeto isn't growing, its because you don't need it. I have a very heavy bioload and all I use is rubble, which I assume is comparable to the marine pure block. I'd do the block and only add the macro if the block isn't enough. The block is low maintenance and you don't have to keep a light on it to make it work. Chaeto on the other hand......
I tried Chaeto one time and while the chaeto didn't grow, the coralline sure did from the light, making my sump and skimmer a pain to keep clean.