I think they are both ok but the first one sounds better.

1. People hold different views as to whether mobile phones are detrimental to children or not. 2. People hold different views about mobile phones as to whether they are detrimental to children or not. In both sentences the 'or not' is too remote from the 'whether': People have differing views as to whether (or not) mobile phones are detrimental to children Actually the 'or not' is unnecessary, since it is implied by the whether. That sentence is much more direct and connected

I agree that the first one is better. It uses fewer prepositions/clauses and is therefore easier to understand.