We used 4 x 4 pressure treated for posts and some corners, with T-Posts( capped) in between and woven livestock fencing. We've since found a source for used telephone poles that are wonderful as corner posts and a now and then post between the Tposts. we buried them about 5-6' down and they're goin' nowhere! Our original turnout areas were done in cedar and that's about 30 years ago. Some have fared better than others, but most seem still useable as we replace them. We didn't reuse them, but they were in not too bad shape.
Nope, we don't recommend them at all. Have seen way too many installs using them
with warped posts. They are not nearly as strong as 4-inch or better posts and round
fence posts are stronger than square fence posts of the same diameter--has something
to do with the growth rings.
I also do not recommend them. They tend to warp and aren't very strong. I strongly believe in doing something right the first time and using these will result in needing to replace posts considerably sooner and spend more money than if you did it right in the first place. We have them here but did not put them in. They are breaking off at the ground and just weak. The nail-in type insulators do not stay in them as well either (kinda soft). For all the new fencing we are using 4"x6' or 4"x8' and are put in using a post driver. Corner posts are 6"x8' with braces. Very strong and no need for concrete. They are round but it is not a problem nailing in insulators and they do lay flat on the surface.
I went the landscape tie route once too, and ended up replacing those posts shortly after due to rot.
I have to say though, I worked for parks one summer and was given the task of repairing an old split cedar fence. Out of about 2km of fencing we only replaced a few posts, and those were mostly ones that had been broken by falling trees. Records indicated the fence was built in the 1930's when the park was a farm! The property was donated in the 50's so there certainly wasnt any maintenance after that till we tackled it - the size of the trees growing around and through it are testament to that. It appeared the posts had the bottoms burnt before planting them, not sure if thats what kept them so strong? Too bad my horses have a taste for cedar, it'd only have about a 5 min lifespan round here