https://teklager.se/en/knowledge-base/apu2-1-gigabit-through... has the necessary tweaks to get full gigabit.

I've applied all of the tweaks and I haven't ever seen it sustain anywhere near 1 Gigabit on a single connection. That's using both a datacenter iperf3 instance and sites like speedtest.net.

Multiple connections can easily breach 1 Gigabit though.

I’ve been using APU2 systems for several years. It can handle gigabit if you’re using Linux and your ISP doesn’t use PPPoE. On PPPoE it tops out around 500mbps for download and 800mbps for upload.

I doubt it.

But if you're comparing with products from Ubiquiti (especially the Unifi line) you're probably going to see similar performance anyway. I switched to a APU2 as my home router two years ago, and I've been very happy with it. Doesn't seem to break a sweat handling a gigabit connection in a typical home setting, running VyOS. I'd probably think about something more powerful in an office or data center.