I lived with a cheap manual pull down for 4 years or so without any waves at all
BUT.....
I also hardly ever rolled it up. I would suggest to go ahead and get the manual pull down
IF You can leave the screen down say when you go to bed/ while your away at work ,if your gone for the weekend etc.
That will keep your screen nice and flat.
I used a 100" 16x9 Elite manual pull down M100UWH I think its around $100.00