At Home Depot today I saw these fence post holders that you pound into the
ground. They go 30.5 inches deep, and taper from about an inch across at the
bottom to 4 inches across at the top. A 4x4 post is held onto the top by a
bracket that appears to be about 5 inches deep.

My concerns:
1) The width of the thing is only 4 inches at the top. Is this wide enough
to not tilt or lean over when you put a 6 foot tall fence, spaced at 8 feet?
2) The entire weight of the fence is held by the 4x4 post sitting in a
bracket that is only 5-6 inches tall, or in other words any lateral force
applied to the post due to wind shear, kids climbing on the fence, etc. is
supported by the end of the post in this bracket - it just doesn't seem to
me to be strong enough.

Anyone ever used these, have any comments about them? Are they strong enough
to support a 6 foot tall wood fence with posts at 8 feet intervals?