Useable every 10 minutes, Convert switches your current HP and MP instantly.
Example:
Before Convert: 803/970 HP, 36/700 MP.
After Convert: 36/970 HP, 700/700 MP.
Convert, the Job Ability itself, produces very little enmity. It's the self cures afterward that can cause you to pull hate.
You'll find mixed opinions among the RDM forums, but the 2 main sides to Convert usage are as follows:
1) Using Convert every time it's ready.
Making the most out of our MP pools, and maximizing potential in a party.
2) Saving Convert for emergencies.
You can be assured you'll have enough MP to deal with links and/or unexpected circumstances.
Common practices:
*Don't stand within a Mob's Area of Effect (AoE) range.
*Try to Convert before you're on the Mobs hate list (Before you cast spells or use abilites on a monster).
For more specific questions on this Job Ability, don't be afraid to ask the RDM forums or send me a PM.