I didn't set anything up 'wrongly' ... it was literally set up with *exactly* the same settings.

All I got from the premium support line was them asking me to bear with technical support because they felt there was a bug there and they wanted to fix it. Unfortunately the company needs an internet connection and we couldn't wait several more days.

I understand it's hard for tech support having to deal with idiots ... but I'm not one of them. I gave them access to the web interface and they could find nothing.

Well, you started afresh and then it worked fine, like it works fine for other users so I can't see why you think it's definitely a router problem or why you're so annoyed!

Why do I think it's a router problem:
It was intermittent
Tech support couldn't work it out - they thought it was a bug
Trace-routes, pings and DNS queries always came back fine
Disabling load-balancing fixed half of the problem

Why am I annoyed
Technical support took 24h to reply properly - and didn't help other than state the bleeding obvious
The routers are specifically designed to load-balance
None of the settings are complex - it should've worked
I shouldn't have to pay 70p a min for support
I wasted several hours on it
I've not 'fixed' the problem - if it re-occurs we have no solution

From a technical perspective, that is not a very compelling explanation, IMHO. It's a complex product; it's not
always as simple as " X is happening" "okay, that means Y is set incorrectly, change it " "Thanks, goodbye".
The problem might have annoyed you, but I don't think your 'anger' is fair. Was your dealer not willing
to speak to you ?