Buy a standard wrist roller if you want, but a homemade version of PVC pipe (1.5 to 2 inches is perfect) with climbing webbing attached is a cheap and amazing solution.
Check our power-rack version that we made out of aluminum tubing. The beauty of it in a rack is that you can truly test the grip without the shoulders giving out first.
With mechanical drop sets, instead of reducing the load, you switch to a new but similar exercise by changing the grip, angle, etc. The result is a whole lot of burning and a whole lot of growth.