One of the particular problems with 28 day cycle is that if you fly one Saturday, then can't fly until Sunday in 4 weeks' time, then you have to find an instructor... I used to aim to fly once a month as that was all I could afford. Whenever I found myself out of currency it was a faff, and often used to eat up half a day.
I wouldn't mind, except that it was always a case of 'yes, but we're running behind. We'll try and fit you in when we've caught up on the next 2 lessons...' I never found it a simple process.