Negligible gains? AutoMc - you may want to read up on this one a bit more.
Of all the mods I've done,
going alternatorless offered one of the single largest MPG gains (10% boost at 70 km/h). It's right up there with the
full boattail (15% @ 90 km/h). Almost all the other mods I've done are in the 2% improvement range. Others can provide similar alternator success stories.
But the operator has to know when/how to use this mod to get significant gains. Simply turning it on/off at various times while driving won't net much (could actually make MPG worse.)
Fuel economy gains will only come from depleting the battery while driving, then recharging from the grid (or other source) at the end of the trip.
Side-effects can be managed. It's not without problems, but it can provide big returns.