I have a similar setup made from rock climbing gear .... been up the mast a couple of times ... I'm 60 and not the most physically fit guy .. make sure the climbing line is tight and the climbing line goes through the middle of the foot stirrups. Mast is 53 feet
I climb my mast using 2 Petzl ascenders, 1 attached to my west marine bosuns chair and
the other to rock climbers foot straps. I secure the halyard tight to the boom vang fitting then go up and down quite quickly and comfortably. The climbing equipment looked better built than the ATN equipment I compared it to back when I assembled this and it was cheaper.
Having once had to be hoisted to a masthead at sea, I resolved never to find myself dependent upon another to get me up and down if the need ever arose on our own yacht. I have owned and used an ATN top climber for 12 years. It only takes a little coordination and good leg strength as one is essentially doing "squats" both coming and going and on our 62' mast, it's a good workout. I use two lines. One for the ATN and a second, companion line, for a mountaineering ascender attached to a safety line that is also clipped to my harness so that if one or the other let go, I'm covered. As noted, however, it is a good workout and if one has not done a fair number of successive squats for awhile, one's legs will feel pretty sore/rubbery for several days afterward.
Another happy ATN climber owner here. I find ascending is pretty easy, it's coming down that is trickier. If you overestimate your flexibility (or lack of flexibility in my case), you can get yourself locked in place. But it's not that hard.
The ATN package is nice b/c it easily doubles as a standard bosuns chair if you happen to have an extra winch-grinding gorilla on board. But it allows for solo climbing, or with the other person just working the safety line.
One thing I find useful is to have a hip belt that I can snap around the mast. This keeps the wild swinging down to a minimum.