Manuka poles etc are great, but cannot be loaded in the same way as a good purpose built pole with a hand strap, unless you have forearms like popeye. The hand straps are essential and you can fully load the pole without gripping the handle hard if you put the straps on properly, see the picture below.
The other issue is the amount of grip, good walking poles have a tungsten tip on them which grips on angled rocks, a manuka pole would not provide nearly the same amount of stability in the rocky areas.
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