Only use the concentrated Holts/Prestone -35C stuff (similar product in different bottles and usually about £4 for 4-5L which makes 50 litres from Costco) in mine, and have done in all my cars since 2000. Not had a blockage in over 200,000 miles!
Don't rate the 'All Season' stuff though, so stick to the 'winter with deicer' version.