As it is, some speak of the virtue of ESF transmutation's bonus to zoo spells and how it allows for easier gearing.
This is at best a lie with a nice coat of paint.
In practice this often means that one is susceptible to losing a lot more to dispels, and their "easy gearing" is actually "lazy gearing" and they often will want to instead gear as if they didn't have ESF transmutation for the security and safety it provides against dispels or other such effects. It creates bad habits relying on the greater amount of zoo bonuses, and this is particularly noticeable on classes such as b.cleric or b.fvs or melee shaman who might want to go transmutation for the mechanics/flavor.
With this in mind I would want to suggest an addition or change: Instead of or alongside making zoo spells d4+3 with ESF transmutation, either revert it to d4+2 as with GSF transmutation or keep it but then have ESF transmutation's presence give a soft +1 to STR, CON, and DEX to the person who possesses it.
This may seem radical to many, but this would truly allow for easier gearing and a boon in particular to the classes who might want these physical stat buffs without them merely losing more when dispelled. If it is changed such that the buffs become d4+2, then it could also be that summons get a soft +1 when summoned
However, I believe merely giving a soft +1 to physical stats allows for said easier gearing that benefits the aforementioned classes.