In a nutshell, I've bonded two separate internet connections together and am achieving not too far off twice the speed. Both lines sync at the full 80/20mbps and are with Zen internet. These connections are effectively bonded and not load balanced (a single connection can achieve full speed).
On the home side, I'm using the Zen supplied Fritz!box router/modems (using my own AC68U for WLAN) and running some software called openmtcprouter on a Core2 Duo powered Dell Optiplex 780 (can be picked up off ebay for <£50). I'm then using a VPS rented from Digital Ocean to join the connections back together out on the internet.
Setup was suprisingly easy. Just really a case of having each modem on its own subnet, running the openmtcprouter installation script on the VPS and adding in the details into your local openmtcprouter machine (based on OpenWRT so has a nice web-based UI).
* Little overhead
* Very easy to setup with some basic networking knowledge (if you know what a subnet is and SSH to a Linux machine, you'll be just fine).
* Works well "out the box"
* Little impact on latency (gaming seems fine)
* Expensive - Two broadband lines are an expensive and might not be an option for some. The VPS is about $5 a month and gives 1TB of usage.
* The connection seems to take a little time to max out both connections so it's not quite as good as having a single connection of the same speed.
* It does work with mobile broadband but the slightly up and down non-consistent nature does hurt performance and reliability.
* Some websites don't like you browsing from server IP addresses (especially Digital Ocean) so may block access or trigger CAPTCHA.
Hopefully this is of interest to some of you or perhaps you may even have some suggestions.
Edited by Benjanyan (Sun 13-Dec-20 14:58:21)