This is more criticism on how the pieces should be represented, than on the rule. In particular, whether the right or obligation to convert still exists should be 'hidden' (like castling rights) or explicitly visible. E.g. when playing with woodware, one could put the Bishops initially on a Draughts chip, to indicate they can convert. When one of the Bishops starts as a Wazir, you remove the chips from both. When it starts as a Bishop, you move its chip under the other, so that it stands on two chips, indicating it now must start as a Wazir.
This is more criticism on how the pieces should be represented, than on the rule. In particular, whether the right or obligation to convert still exists should be 'hidden' (like castling rights) or explicitly visible. E.g. when playing with woodware, one could put the Bishops initially on a Draughts chip, to indicate they can convert. When one of the Bishops starts as a Wazir, you remove the chips from both. When it starts as a Bishop, you move its chip under the other, so that it stands on two chips, indicating it now must start as a Wazir.