I have one. I am a very big guy to climb a mast and like you used a separate line for the ascender and climbing harness. It worked very well. I would not climb it without one. If your main halyard
is old I would sew a new line to the end and pull it through and climb on the new one. Once you get in the rig pull out the slack and put your weight to it a few feet off the deck
to get the strech out of it.
It's nice to be able to shift your weight from feet to bum.
Put your tools in a bucket and take a lifting line up with you to haul them up when needed. Keep kids
and bystanders away incase you drop something.
Also use a waistline to keep you close to the mast. And take your time.