How is it partnering with UwU Market?

I'm looking into getting VTuber merch made and came across this website, but I can't find the information I'm looking for.

How do they determine who they partner with, and are they open to partnering with smaller creators with potentially limited demand for merch?

What's the process for getting specific merch items made and sold through them?

And have creators had a positive experience working with them? Are there any major issues they've run into?

Thank you in advance for the info!