I guess it depends.
We had slide toppers on our previous 2 trailers and had a time with wasp nests and mildew in places we couldn't reach and the upper seals dry rotted because I couldn't treat them.
We had Colorado brand and they never failed.
Our latest trailer doesn't have toppers and can't say I miss them.
I must admit though that I'm quite anal about cleaning the roof and slides monthly and applying 303 on the seals.
Was actually surprised at the amount of buildup that accumulates under the toppers over time.