I have used a tree saddle for several years. I wrote a couple reviews but I can't get them to come up in the search engine.

In summary,

Pros
You can hunt any tree that will hold your weight. The weirder shaped trees make great cover.
You can use the tree trunk as cover keeping it between you and the approaching deer.
You can shoot 360 in silence.
You safely doze in the saddle without fear of falling.
No one can hunt your stand without a saddle.
No one will probably even ever know the spikes are there unless you show them.
The saddle has a loop on the back to function as a traditional safety harness.

The only real con is that it is almost impossible to sit in one all day because they are not as comfortable as good climber or lock-on. If you are overweight by more than a few pounds then forget it.