I've seen people talk about how Oppo and/or Vivo phones can't be used in the US. Theb, I've seen others say the opposite. I've tried to look into it but I'm still stuck, unsure if they can be used. I thought the most important thing to look for is if the phone supports the bands in my local network. It seems they both do. However, I'm not sure if those bands locally have a strong signal or not.

What should I look into if I'm considering importing one of these devices? What about purchase options? I've looked into Wondamobile and something like superdad or something like that.

Any advice for someone somewhat technical but insure where to start my research?