I have the Tektonik RUTX11, which can do all that. The RUT950 can do that too, but it only has Wifi4 (b/g/n) and no Wifi5 (ac), and that's a bit slow if you want to stream a film and are a bit further away from the router. I have a public free WiFi in the mountains, and I use the router with this free WiFi to make a NAT subnet with its own WiFi. It works great, I have my Sonos in it and do AirPlay on it via my mobile phone, Netflix Apple TV, etc. So it's highly recommended. So it's highly recommended. I haven't tested SIM yet, but I think it works perfectly. You can split WANs (2x SIM) / failover etc. in the admin. I send all traffic via nordVPN, as the public free Wifi (my WAN) is not encrypted.

Hello, yes, you can do this with the router via the WAN FAILOVER menu. There you can set when and how it should switch to which access point. I just don't know exactly how it is with public free networks regarding e.g. AGB acceptance. There are networks where you can get in without a password but then have to log in via e.g. AGB.