I use a 3:1 exclusively. I can go hand-over-hand for a short distance, two hand pulls almost continuously, or use a double-handed ascender with foot loop when I'm away from the trunk and want to go faster.
I depend on my ZigZag, but I always keep at least one hand on the rope below it until it's taken the load. The hand ascender provides a backup when I use it, but coming down with it would be difficult and slow. I'd rather just use my gloved hands on the rope, and stop or switch hands if/when they get too hot. That's doable with a 3:1, but probably not on SRT.
I just cannot get comfortable with the idea of using a foot or knee ascender. If the ZZ were to fail, I'd be in a very awkward position with the ascender jammed against the bottom of the ZZ. That beats falling, but not by much. I always tie a knot in the rope when I'm twenty feet up to prevent a free-fall to the ground.