Regarding saturation time,

Most ignition amplifiers automatically find the saturation point for all operating conditions
by measuring the current drawn and averaging it over a few sparks.
This maintains the most efficient coil charge dwell time all the time.

However, most ecu's that have INTERNAL ignition amps have fixed or variable dwell times
that need mapping or cannot be adjusted to provide the same
job - then coil type can be an issue to worry about.

IMO, External amplifiers are always supperior for this reason and because also
less heat is generated in the ecu and electrical noise is confined within the engine bay.