Paying 'up front'.
Hi sigibbons,
I would say buy your lessons one at a time to begin with, until you are confident that you have both a good, regular instructor and a good club. Then, and only then, buy blocks of never more than 10 hours.
At some places, for example, you can find yourself flying with a different instructor for every flight, no matter what promises may have been made to you before hand. (There is always a 'reason' why your regular instructor can't fly with you). Don't tolerate this for a moment; move to another club. This is one of the reasons why you do not want to be tied financially to a particular club until you know they are going to treat you fairly.
Under no circumstances buy a whole PPL course, paying up front, because if you do they have got you by the 'short and curlies'.
Remember also that flying clubs in general operate on a wafer-thin profit margin and are apt to go bust suddenly and with no warning.
Broomstick.