I've had good luck with Harris, but make sure the one you get allows the rifle to cant, since you're shooting from uneven ground, and not from a flat bench top. Usually there is a friction adjustment so the rifle can be canted, but isn't free to flop around. Choosing the correct leg length can be challenging. If you choose too long, you can't shoot from prone on flat ground, if you choose too short, you can't place the legs over the crown of a hill or a mound.
When it comes to using a bi-pod, when shooting from a hard surface like a rock or frozen ground, I prefer to put a soft material between the feet and the surface of the ground to prevent the rifle from shooting away from the hard surface; just as you would intervene your hand between the forend and a hard surface when holding the rifle in your hands. I tend to use my gloves, which I usually have with me, between the feet and the ground. On a soft granular surface like sand, gravel, or dirt, the legs are inclined to work their way down, which while increasing stability, will eventually interfere with your ability to aim. Increasing the surface area of the bi-pod feet, again I use my gloves, might be beneficial if you fire multiple shots from the same spot on soft ground. Rather than the common practice of placing your support hand under the butt of the rifle, which admittedly is a useful means of elevation adjustment while aiming, grasping a bi-pod leg, or placing your hand on top of the scope, might help prevent rifle bounce, which will increase your hit potential, and enable you to reacquire the target more quickly. You'll find your reticle will appear to be more solid on the target if you load the bi-pod legs with forward pressure, so once you assume prone, push forward slightly, until the rifle no longer pivots on the bi-pod. If you do this every time you shoot, you've built a bit more uniformity into your technique, and uniformity pays dividends on the target.