Silent: Electric vehicles do not have noisy engines. Instead they have motors. The only noise from a motor is that of the moving parts.
CO2 emissions: These are cut completely as are all other harmful emissions emitted by combustion engines.
No fossil fuel costs for the owner: The wild fluctuations in fuel prices are no longer a problem. You charge by simply plugging into a normal wall socket. Electric prices are typically fixed for months in advance. Typical electric bikes cost less than 1p/mile to run.
Cheaper parking in London: Some London boroughs are now offering free or reduced price permits for electric vehicles. This can be a massive benefit.
Road tax exempt: Electric motorcycles do need to be taxed in order to be road legal, but they are free to tax. They are also congestion charge exempt.
VAT back: The VAT on electric motorcycles can be claimed back by businesses.
Cheaper insurance: Insurance on electric vehicles can be considerably cheaper than on their combustion engine counterparts.