What make & model have you ordered? I have two electric items; and old B&D GA100 and a newer B&Q FPIS2500. The B&D item is very reliable and will shred pretty much everything I wanted up to around an inch diameter but few spares are available now. The B&Q item was bought as an emergency replacement for the other whilst making repairs; it's OK with wood, but clogs up with any volume of leaves - not a good item.
I've not had the need for a more powerful, petrol, shredder and have little knowledge of them.