The ATN product is basically the same as what mountaineers use for vertical ascension.
Pretty sure you can buy them at REI.
I prefer using a set of falls with 4:1 purchase
Divide your weight by four. If you can pull down with that much force you can pull yourself up the mast safely and easily with no assistance. Best thing about is that you are always in complete control.
To assemble your falls you will need 1 double block, 1 single
block with becket, and a line that is the height of your mast X4 (get blocks sized for 1/2 inch line). Block with becket attaches to the chair, double block is raised to the masthead with main halyard
When you get to a height at which you want to stop to work simply bring the end of the line that you have been pulling on under the D-rings at the top of the bos'n chair and wrap a half-hitch around the falls. Add another half-hitch and you are seriously locked in.
My falls are set up with 1/2 yachtbraid so it is easy on the hands and has a working load of well over 1000lbs so I don't shy away from that second helping of pasta.
Can also be used as a 50 foot-long vang!