Been trying them in different designs for a bit. Need to be really careful though. Lots of printed parts can have weak spots where layers didn't bond as well as they should. These parts can fail catastrophically, Be careful. Some things I've learned that might help others trying them,
Print out of an Engineering material ABS at minimum, PC-ABS, PC, Carbon Filled PC you get the idea (Don't attempt in PLA it fractures easily and doesn't hold up on cold) **VERY IMPORTANT**
Do not rely on thin sections for strap, Best to have strap compress the part against tree rather than part cantilevered out away from the strap
A metal reinforcement small bolt or such through middle can keep layers from separating by compressing layers together (don't crush) also provides a small safety if part fails tends to do so slowly possibly bending bolt but giving you time to react instead of a shear and you fall
Print several layers on the outside, this makes continuous external loops verses one loop on exterior that can fail then you rely on the inside that is choppy to hold it together.
On the same count as above use thinner walls with lots of support ribs, this keeps stress in the part when building lower and allows more continuous threads to be laid down increasing strength.
Check parts often for cracking spiting discard at any damage, not worth it. Also watch for weathering plastics are susceptible to sun damage especially in the south.
Adding holes in tree side fore small hex head screws can actually help the step bite into bark, but also can keep tree from getting ripped up as much by reducing sliding around.
Lots more i could add for sure but these came to mind pretty quick, hope it helps
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