Hey bud,
I personally use the Prime fitness wedges.
Product will ship in approximately 10-15 working days. By elevating the heel, these PRIME Squat Wedges enhance a user's ability to maintain proper squat form for any body type. Choose from a 5 Degree Incline up to a 30 degree incline. All PRIME Squat Wedges are 30" wide to facilitate both...
primefitnessusa.com
They are a good aid if you do not have the ankle flexibility when doing squats where you are trying to target the quads. The anatomical position that the elevated heels put you in, allow for greater flexion at the knee joint while still driving through the entire base of your feet. (ie. without the wedge, you would be up on your toes when trying to close the angle/gap between your hamstring and back of your calf). Similar concept to wearing platform shoes with a raised heel or the old school method of 5 or 10lbs plates under the heels of the foot. You will notice with using a wedge, your entire foot is still making contact with the surface plate of the wedge which adds to the stability and power draw through the entire movement..... (as opposed to say just using a 5-10lb plate on your heel and having a gap between your foot and the ground right in the middle of your foot).
Depending on just how bad your ankle flexibility is, would determine the angle of incline you need to purchase.
I also personally flip the wedges around and use them for SDL's and RDL's. It allows for me to start the deadlift in a pre-stretched position once I unrack the weight, which as more and more science is reinforcing , leads to better fiber recruitment and motor-unit activation.
Hope that helps.
AE