The 303 has worked for me for many years. Maybe it depends on what kind of contamination you get on the windshield. Not too many bugs here but a lot of bird droppings..I would not recommend the 303 windshield washer tablets. I tried them several times, and was never impressed with the results. I tried them to the instructions the first time, with only average results. So I tried using two tablets to a gallon of water. Still only average results. Then three to a gallon. No noticeable improvement. I tried adding them to the cheap windshield washer fluid, thinking they may boost the performance. No noticeable improvement. Don't waste your money. There are better options out there.
I have used Nextzett Kristallklar Premium and have been very happy with the results. It does a great job of cleaning the windshield. It does not have any anti-freeze ingredients, but they show a water/alcohol ratio for different temperatures. I would highly recommend this product.
After reading excellent reviews, I recently bought a bottle of the BMW windshield washer concentrate. I haven't tried it yet. But it has the advantage of having antifreeze additive in it, so the back label shows multiple mix ratios, depending upon the freeze point desired. If the reviews are accurate, this should be a great option for a windshield washer concentrate.