I have no idea of a suggestion to buy, but in will say the power plate at my gym has been one of the best bits of kit for my rehab following knee surgery.
I've used wobble boards and bosu balls, squatting on them etc with a plan from my physio. Holding a squat on power plate at certain ranges of movement has definitely been the best way to hit the muscles around my knee.
I lost a huge amount of muscle following a procedure called microfracture for a cartilage tear of my femoral condyle over the weight bearing surface and it has been incredibly difficult to build it back up. I can only now run 1 year after surgery.
The power plate I find especially helpful at targeting my VMO and I can actually deliberately engage this now, when I really couldn't before using the power plate