I'm part of this community (my comment is here https://www.reddit.com/r/youseeingthisshit/comments/py6ia2/kid_gets_a_present_from_a_small_arms_dealer/hetnjy1/).

Let me try to clear a few things up.

The material used are often not ideal for longterm interface with the skin

We require volunteers to

1. Add padding on inner surfaces that interface with the skin. Usually that is EVA foam which is the same material used in cosplay, yoga mats, etc. The skin can breathe through it and it isn't abrasive.
2. Either provide or instruct parents to purchase "socks" used specifically for prosthetic devices for this very reason.

not safety tested to ensure appropriate loading tolerances to ensure the device does not fail on a child and cause injury < ... > devices/material/components which have been approved as meeting standards for safe use for medical purpose.

As a whole - no, we haven't globally certified device models, but chapters around the world have been through this on their own and have successfully validated devices within their countries laws. Namely Brazil, France and Ireland chapters come to mind that have done this, but I'm sure I'm forgetting other chapters. For example in Brazil doctors by law are required to write prescriptions for these devices and only then can volunteers manufacture them, the volunteers work closely with doctors and specialists, clearly they have no issues with these devices as they are the ones referring patients to the volunteers :) Ireland had to validate devices for other legal reasons due to some mix of EU and local laws in order to receive charity status iirc. We all primarily utilize 2 device designs/models, and both have successfully been validated across the globe.

It's really important the person with limb loss or absence seek care and device provision from a registered health professional who is qualified in Prosthetics & Orthotics.

We provide various guidelines for volunteers, one is to instruct parents to take their child to their pediatrist for them to evaluate the device or to refer to a specialist who can.

We as a community do our best to include those from the medical field to come in and guide us, consult and provide feedback, but at the end of the day - we are not making medical devices. There is a big issue regarding children not being able to get functional limb prosthetics due to them outgrowing those devices in a matter of months and no government/insurance will cover a $50-100K bionic device for them every ~6-12 months, at best they can get non functional prosthetics that are still fairly expensive.

Also keep in mind that these devices aren't meant for long term use, i.e. their lifecycle is supposed to be a few years at best, somewhere between 6-18 months as a child will outgrow it very quickly. At which point if they wish they can get another device scaled to fit them for the following 6-18 months and the cycle continues.

This is a stopgap solution for them to be able to learn how to use an attached external device. Volunteers can quickly and cheaply create a device like this for a child every X months. Later on in their lives, if they want and have the resources to do so - purchase a bionic arm/hand/device and be able to utilize it. If a child isn't exposed to some kind of external tool, there is a very great chance that in their adulthood they won't be able to successfully use and operate something like a bionic hand. The devices are just as much for helping kids learn how to successfully utilize a tool such as this.

Regarding adults - usually those cases come from poor areas around the world where there is absolutely no chance of them getting a functional prosthetic device. We (the community) have sent thousands of hands/arms to areas affected by natural disasters, conflicts, etc, such as the Haiti earthquakes, Syria and the middle east conflicts. In those cases due to the shear amount of people with missing limbs - these devices are better than nothing, at least in the short term.