Wil not hurt the brush, but will taint it if being used also for WFP, you can apply the TFR with a pump up sprayer, or if higher use a separate backpack and brush and mix your solution up in that so you can apply it using your WFP.
We are working on a Budget option at getting chemical to height, should be out in a month (will also be able to be used to get water to the Easy shine at height)