Phil,
Thanks for your comments. I have done a bit of homework and found out that for 3 Fujitsu General heat/cool inverter units installed Polaris are approx 1000 euros more than local installers but I can't tell if the local installers prices include installation of the power supplies. Either way, Polaris is more expensive but for ease of arranging and warranties, peace of mind etc I'll probably use them - absolutely no grey areas that way!
I'm about to see if Polaris will let me pay a deposit for the installation now and the balance on completion in July. I'll let you know what they say.
Regards
Tim