Admissibility in court feels like the barest minimum of requirements here, to say nothing of the other services like counceling the linked thread discusses.
Yes, but having the option to admit this in court, including of course the choice to NOT admit it, to stop all proceedings, in the justice system and/or court seems equally the barest minimum of requirements. Including the option to deny anything happened everywhere. To avoid and/or dealing with counceling (or God forbid, CPS. There's plenty of children and adults who are terrified of dealing with any official at all because of their experiences with CPS. They, frankly, have good reason). That's the requirement that I think this private rape kit does better than the official one.
Except DIY kits are not an option to admit in court. They are not admissible. There is a temporary order allowing them to be collected during COVID-19 in California only. It is yet to see if these will even hold up.
None of that matters in civil proceedings, like divorce or child custody hearings. Even pictures of Facebook chats are admissible there. If those are more important to you (even if they're not happening yet), I would still understand the choice to go for these.
Furthermore, admissible only matters to a limited extent. It means someone won't go to jail based on this evidence alone. It doesn't mean it doesn't get considered at all. Even then, there's hacks, you could have someone from the company testify to the results of the kit and what the results mean, for example.
Using these kids deprives the government and public prosecutor of many options and places a lot of power with the individual. That weakens the case, but that may be a good trade for people. I'm not sure giving people extra options between keeping silent and going full-on nuclear with zero control and uncertain result (the government route) is such a bad thing.
I can also see why a person with this job (and the conviction that makes one take a job like this) would consider it a terrible thing.