I switched to the 9010 brush several months ago and I'm still amazed in the difference it makes.
When I pretreat the paper with oxalic acid I do it several days in advance so it is dry when I use it. I have found that if I just let the paper rest for 5 minutes and use a cold air setting on the dryer after coating that I get much better blacks (of course I'm talking about the sensitizer here not the oxalic acid). The added moisture makes a big difference. First couple of times I was a bit nervous, thought maybe the added moisture would mess up a neg but no problem so far. Nothing has plated out on the negative.
Just mixed up a fresh batch of ferric oxalate and plan on doing a bit of testing this weekend.