Try not to look at this in terms of 'off' or 'on', mate. This has got to be a lifetime change if we want to keep it up longterm.
Useing flexible syns when you feel the need to eat more syns, is still sticking to plan (even if you used flexi-syns every day for a whole week!- you are still in control) you might not lose, but you are still following the plan- and it is less harmful than seeing it as needing time 'off' your new lifestyle choice.
I could have done that...I have in the past, but really needed a week without counting syns. I feel refreshed now and much more able to continue starting tomorrow. Am positive it hasn't harmed my overall goal. Just over a stone when I put on today!