I use the blocks and have never had a problem except for soft ground (which is rare in my experience). It's actually pretty rare that I need more than one on any given side. And I've never had them "slide around" on me; they've always stayed put even on smooth concrete pads.
Advantages are that they are light, easy to clean, don't take on water, don't attract insects, don't rot (at least not like wood does), stack nicely in a bag.
Disadvantages are the cost, and that they can often sink into soft soil. They actually do "rot" over time when exposed to UV just like any other plastic, but I have yet to break one and my rig can weigh up to about 9500 lbs.
I say use whatever works best for you. I like my blocks, but I'm certainly not above using wood.
-2018 Greyhawk 29MV
-1997 Jeep Wrangler YJ (Toad)
-2015 Jeep Grand Cherokee Limited (Soon to be Toad)
-2014 Jay Flight 28BHBE & Ram 2500 6.4L CC 4x4 (sold)