As one who has previous knowledge of what it is like to come into contact with a chainsaw (to my shame TWICE) may I recommend you go for the full protection and also follow the link for a bit of bedtime reading - http://www.hse.gov.uk/pubns/afag301.pdf
As a general point of interest suprisingly the HSE web pages on forestry is a good place to look for best practice. I know it's fashionable to take the micky out of 'Elf 'n' Safety' but occasional use can also be as bad being over confident.
Greyman