It would help lift offender's self-esteem and confidence to work, save the tax payer money, increase understanding and respect across society, and reward success (i.e. pay volunteers a 'bonus' if offenders turn their liofe around and do not reoffend.
Why not supervised work teams (including volunteers from across society) instead of a short prison sentences? This could be working to grow vegetables on 'public allotments' (produce grown used in hospitals, prisons etc), make minor road repairs, gardening in public parks or nursing homes. Volunteers (with travel costs paid) could help befriend offenders and be a contact point when they finish their 'sentence' – perhaps even receive a payment if the person they help mentor does not reoffend in a year.