I also have the magnetic mesh net doors that meet in the middle, bought off Amazon. Keep them up all year round and just tie back when not needed and over winter. They work best if when putting them up, if the centre top is lifted just a little higher. This encourages a good 'centre meet'.
They are brilliant and I'd thoroughly recommend them. I wouldn't buy just the cheapest you can find in case of poor quality.
Although my two meet magnetically in the middle, it is actually one unit, ie one piece.
Mine cost £17 for the standard back door size.