It will bounce a little bit on hard ground, but it still works OK. Remember, your foot is stomping down on it as it throws the clay, so it isn't really going anywhere. The worst that happens is it gets a little bit off-kilter. You may want to re-align it between shots, or you may not: Letting the angles change keeps things interesting.
On soft ground, the front end digs in deeper and deeper, which means it isn't throwing the clays as high. Also, once the front legs dig in, you can't change the side-to-side angle without picking it up. With the two-by-four, you just nudge it with your feet to move it from side-to-side for a new angle.
I'd say just get it and do the modifications you need to make it work with the terrain where you mostly shoot.