VW 502.00 is the Non-Longlife regime specification oil for gasolene (petrol) cars and is safe to use for the MK5 GTI. Pretty sure they suggested using this spec oil for fixed time and distance servicing if you look in the owners manual if I recall.
As Quantum Platinum Plus has type approval this means that it has been tested by Volkswagen themselves to meet certain criterias such as sludge performance, wear properties, ash output and others. Not surprising really as Quantum is a subsidiary of Volkswagen UK!
I've been using VW 502.00 spec oil for about a year now - Mobil 1 0W-40 FS in my 2005 GTI (115k) and its been running great for me. It's actually a lot smoother on startups (especially in winter) and I don't need to top up that often compared to the VW 504.00 5W-30 longlife oil I was using before. Even did a 1000 mile trip to the Nurburgring and back in 35c heat in the summer and it hardly used oil (just topped up a smidge to my surprise). Pretty much sold on the stuff and recently did an oil change with it again in preparation for winter!
So overall that oil should be fine.