Happy to help ;)
If you are going to ingest the powder directly, I'd be inclined to buy it ready-made.
I only use Buhner's recommended sources and checked 1st Chinese Herbs for Gou Teng powder.
This is what I would buy:
1stchineseherbs.com/uncaria-rhynchophylla-vine-with-hooks-powder-gou-teng-plum-flower-powder-1lb/A mortar and pestle will not make a dent in Gou Teng. The parts of the herb that are used are the vines and the hooks - both quite hard.
When making tinctures, I grind my Gou Teng vines and hooks (your 2nd link) with a coffee grinder. The end result is not something easily swallowed.