I've been using this for around 6 months now to aggregate a 70 mbit FTTC connection and 150-450 mbit 5G connection; overall it works pretty well. The FTTC connection is the "master" link and it seems is preferred for the first several bytes of the connection, so the latency is better than using the 5G connection directly. This provides a nice balance for general web browsing, as loading web pages is still quite quick and overall download speed is more than either connection alone. In my setup I'd say it's about 80% efficient in terms of aggregating the total download.

There are a lot of configuration options and the stability of them can be an issue. I've found using XRay VLESS for the Proxy and Glorytun TCP for VPN to offer the best overall speed and reliability. (Edit: I've disabled SQM too). It's possible to mostly bypass the VPN by enabling proxy UDP over XRay but I found that breaks various bypass rules, e.g. so that Netflix connections always go over 5G, as some content has restriction from being accessed by my VPS data center IP.

Port forwarding is also a bit hit and miss; I have configured my 2 WAN routers to use the OMR router as a DMZ and then if I want to play a game, or enable remote access, I will use the bypass feature so that the device's MAC goes through my FTTC connection. UPnP works correctly in this scenario which is handy for consoles.

I've never heard of XRay or V2Ray. It seems like a niche thing?