

The ones on Amazon are intended to run GPUs for crypto farms, but they’re all brands you’ve never heard of with dubious claims and they’ve all got at least one review where either the device was defective or something was installed incorrectly and it caused damages.
VLANs are lower than IP so you don’t need a router to have a VLAN, but you will need a router to get packets between the networks. I don’t think a WiFi repeater works. You likely need separate WiFi client and AP devices so you can put your WiFi on a different channel. Otherwise you’re probably halving your WiFi performance when connecting to the other network over the same airwaves.
Unless you can convince the other network to route your IP addresses, this setup will give you another layer of NAT and may cause problems with online games.