What are the main features and functions to look for In an aerator?

•  Strong metal tines or spikes 

•  Curved blade type spikes – claimed to have the advantages of spikes and tines

•  Galvanised steel spikes, or tines for rust resistance

•  Transport wheels – possibly with pneumatic tyres for grip

•  Lever controlled lowering and raising of tines/blades

•  Ball bearing mounted wheels for a smooth run, even after seasons of use