Heh, this is almost thread necromancy.
As far as 'hardly any benefit' goes, for a feat you're getting a power that is more powerful than what it is replacing, plus the benefit of a feat's worth of bonuses, plus the ability to increase the power of it over time.
And capturing a familiar wouldn't be very easy. Even if it's by itself, it has the master's defences and the ability to attack and escape. If it's with it's master, then it's not targetable, so you'd have to kill the master or capture him to get at the familiar, at which point you have the power to kill him anyway.