I'd get the VW part unless you're replacing both and feeling lucky! I remember a guy at work getting new springs on his car, got aftermarket ones. Front of the car sat higher! Looked idiotic. Never mentioned it to him and I'm not sure he noticed.
Hum, I did that to my daughter's 2009
Ibiza while I was looking after it for a few years while she worked aboard, naughty car broke a front spring as we drove to the airport for a week's holiday abroad!
To be fair, the 2009 1.4 16V 86PS
Ibiza SC was always a bit "up in the air" when compared with my wife's Polo, but ECP's chosen Sachs part number was not correct for that car.
I bought Lesjofors front and rear springs for my wife's 2015 Polo, via Autodoc - I picked the part numbers, getting the right fronts was easy, couldn't find the correct rear ones so just grabbed the closest one, the fronts were spot on, the rears dropped the rear by maybe 10mm, which actually improved the stance of the car and mainly it is only 2 of us that are in it.
So, I checked out ECP for the correct Sachs offering, as soon as I saw them on the counter I noticed that they didn't have the usual format of numbering that official genuine Sachs parts have - they had the Lesjofors format along with the DOM code - just exactly the same items as I had bought from Autodoc - so I just returned them. When I contacted ECP's
help line and asked about this and included the correct Sachs part number, I was told to pass this to my local ECP branch and they can very easily source them for me - did they? Not at all "we don't do that sort of thing" - oh well I tried, I probably would not have liked the price that genuine "not normally stocked" Sachs springs would have cost me from ECP!