I have a Geissele AR15 reaction rod and while I think it was pricey, I have gotten my moneys worth out of it. Since I bought it the price has gone up to $100. If I had to replace it I would probably just buy the Magpul BEV Block at half the cost.
Recently I wanted to get something similar for the 308. The Geissele AR10/SR25 reaction rod is $200, which seemed a little high to me for a splined shaft. So I looked around and saw that Brownells had a knockoff for $50. At one quarter the price I quickly purchased it.
I learned the catch. I guess Brownells wanted to change the design to avoid copyright or patent issues, so they removed the vise flats and put in a square drive.
Their instruction tell you to put muzzle device or barrel nut wrench in the vise, install a torque wrench or breaker bar into their reaction rod copy, slide their reaction rod knockoff into the action, and precariously balance the upper between your wrench in the vise, and the wrench in the reaction rod knockoff, and torque it all down with out dropping anything. Good luck with that.
I found I could sometimes clamp the round rod in the vise tight enough that I could use it like a Geissele reaction rod. I finally ended up just milling some flats in it so I could secure it in a vise.
Unless you have the capability to put a flat on the Brownells tool, I’d recommend passing on it.