The Superheadz Holga 35mm adapter is Superheadz's version of the 35mm adapter, designed for use with cameras in Holga 120's range (N, CFN, GCFN and PC to name the few)
The price difference between this and the standard Holga 120 to 35mm adapter comes with a reason:
The question of whether you really need this comes down to how much you will be shooting your Holga 120 using 35mm.
If you have a Holga 120, and have thought about getting a Holga 135, then yes, this is definitely for you as the 135 can not shoot onto sprockets.
If you want the best of both worlds (120 and 35mm) then getting the Holga 120 and also having this handy sure beats the original adapter by a mile and will make your life a helluva lot easier!