Fire toasting is inherently inconsistent as it varies within and along the same piece of oak depending on surface impact of the heat (toasting is the outcome of time and temperature, vary these elements and the resulting toast varies as well). This creates aromatic and flavour complexity however, at the cost of consistency.
Convection toasting is controlled and measured and produces a uniformity of toast throughout the same piece of oak. The same level of toasting can be replicated infinite times, ensuring consistency from batch to batch. The cost of this consistency, however, is aromatic and flavour profile simplicity.