This is wrong. First, the UDM is not discontinued- it's for sale right now. Second, you don't need a USG+key to do VLANs. You do need to run a Unifi controller, but you can self host that anywhere like on a RasPi or in a VM. You don't need a USG to do the tagging and routing, either... the VLANs you set in the Unifi controller will work with any router/gateway it's just not all streamlined into the controller interface if you use a separate gateway. I know this because I do exactly that, I have a pfSense gateway and Unifi switches/APs.
VLANs are at layer 2 which is switching. Routing is layer 3.
I have several Unifi switches and a controller (running on an rpi) on my network but I use my own router. I can setup VLAN access ports and trunks all day on the switches no problem, but I can't control the layer 3 routing between those VLANs with the controller, which is what you're talking about. By setting up a gateway/network on each VLAN from my router I can control routing. It's just not as slick as having a USG where it's all controlled via the controller UI.
A couple of their top of the line switches can actually do layer 3 switching. I haven't actually tried that, but the docs don't mention it requiring a USG so I don't think it does.
Yes. As I said, I do that myself with a pfSense firewall/router into Unifi switches and APs with multiple VLANs and routing between them. I've also done it with an Edgerouter + Unifi switches and APs, and a Mikrotik router too. Of course the Unifi controller doesn't control a non-Unifi router, but you can set up whatever VLAN arrangement you want in the Unifi controller and then set up your router to match and do whatever inter-VLAN routing you want separately in its own interface.
It is not all nicely integrated together if you use a separate router (obviously), but it's not like it makes it impossible. It's not even difficult... at least not any more than it would be in any other setup.
Same here but with opnsense instead of pfsense. It would be great to have all of the info in the controller's dashboard, but I wasn't thrilled with what ui had available over the last year and figured I'd punt buying a usg or similar down the road a few years.
I personally wouldn't recommend it, the USG and their other Unifi gateways are actually kinda limited feature wise. You get all the stuff in the dashboard, but I'd say it's fairly primitive compared to what you'd be used to in ***sense. It's a good solution for people who want something turnkey, but if you're a prosumer/homelabber type you're better off leaving switching and APs in Unifi but using something else for the gateway. I do quite like the EdgeMax routers like the ER-4 paired with Unifi, however. Just my own perspective having tried all of the above.
