with all the negative reviews about being hard to work with, did anyone actually dig this stuff down into the ground as the instructions say?

It is not going to separate mulch and concrete if in the ground! The stakes really are pathetic, but it may be possible to bolt them to the edging. You also need to bolt the pieces together if you want it to work, I suspect. Have not tried that yet, as I am still deciding if this "product" should be returned!. Some of it has actually been useful. I have used it to separate a wood walkway on a bayou from mulch by using screws to connect it to the wood. That is the only way it has worked well so far. The spikes are useless without modification if you want the edging to stay in place as instructed. Even when you lay it in the sun and put large rocks on the ends, the ends will not straighten, even though the rest of the edging body will!