Is online divorce a con? Whats cheapest best way?

My partner and his ex wife want to divorcee. All very amicable, no house or children. They grew apart married young he in army etc, no nastness in anyway. We been looking at online divorce, is this good or con, is it the cheapest? Any ideas. They only thing he wants to do is protect his pension, she hasnt mentioned wanting any of it. Any one have advice best cost affective way?