keep in mind that the final reserve fuel is equivalent to 30 min hold, it does not mean you will do a 30 min hold with it. If you hold at destination ,using it, then you are commited to land at your destination,no matter what. You have no choise of diverting after you've used your final reserve, as you will arrive at alternate with fumes in reservoir.
If you divert,then when arriving at alternate you'll have fuel for 30 min, starting to use it means a mayday call. So, I doubt you'll use it in hold.
Don't put yourself in the corner, using the final reserve at destination.For us ,minimum at destination is final plus alternate. If you expect less than that,then a technical stop would be required. Followed by tea and biscuits,of course..
