I say if you like them go for it but generally grapes have a lot of sugar, so freezing is a good way to portion control them. I imagine cotton candy grapes may actually have a higher sugar content? (bred for sweetnesss) but who knows.
Edited to add: I was able to find it. They are slightly more caloric at 50 calories per half cup vs 31 calories per cup of regular grapes. I am guessing that grapes calorie count is an average though because I'm sure some grapes are less calories than others (like I find green grapes pretty sweet but black grapes seem less)
You can't out-exercise poor eating habits.