I've moved this to it's own thread Davro, that other one was about inverter machines and Portamig/MTA/Techarc are mainly transformer based unless you're talking about tig welders in which case they do both transformer and inverter based ones.
What type of machine are you enquiring about?
They are all made by same people;Technical Arc Sevices I got a 211 via Rapid Welding in southhampton £500 inc vat and delivery with a genuine binzel mb25 and regulator
I think model for model they're all pretty much the same internally, the only difference might be the quality of the torch and regulator supplied by the seller.