My experience has been a little different:
We've had 2 TTs; one with and one without. On our current one, we had them installed prior to purchase. My experience (going on year 4 with them) is that they are fantastic. I have never heard ours make any noise or flap -- (maybe that is an adjustment issue?) -- and we've been camping in some pretty windy conditions.
Bottom line (and just my opinion of course!) is that I wouldn't be without them. Saves you from having to get a ladder and try to brush off any twigs or pine cones or other debris with a broom (while simultaneously balancing on that ladder) that get on the slide top prior to closing it. You'd be surprised at what accumulates up there that you can't see from the ground.
Also, depending on where you camp, it can be pretty tough finding enough room around the slides to open up a ladder at all (trees, hills, etc., around your spot).
Good luck with your decision!
2016 American Coach Revolution 42T
2004 Jeep Wrangler Sport