I've had a turbo back blueflame system fitted for nearly 5 months and had no problems at all. I've only heard of the hanger weld becoming broken on the LCR systems not on the 180 Cupra's like mine. I've had the car remapped after it was fitted and that has been nearly 2 months and all is well.
Personally for a 'budget' system, I think its great, good sound under acceleration. Stainless steel is stainless steel, to the untrained member of the public they would notice minimal difference in quality between that and the Milltek system, just the overall finish is probably the main one. But for a turbo back Milltek? £1000? Thats alot of notes....