This is what I can tell you about Improved Feint
1)Improved Feint is an attack and as far as I've experienced, that attack happens with no more delay than any other special attack. Maybe the people who write concerning IFs unusable delay are writing about Bluff, which does have a long animation delay and while it isn't good in combat, it requires no feats and is great for pulling single targets around corners or away from door ways/switches.
2)If you freed up one feat and are interested in Improved Feint, either you already have Combat Expertise or... well, why are you asking if it may not be worth two feats when you wrote that you had only freed up one feat and wondered if IF would be a decent choice? I ask out of curiosity and a desire for clarity more than out of pique: Do you already have CE or not?
if you already have CE then try IF and see for yourself if you like it. Its 3 days and a sibery's shard to switch out.
if you're trying to decide whether or not getting IF can justify keeping CE, rather than ditching CE and grabbing some other two feat combo... well, what combos, pls
if you're trying to decide whether IF is worth switching out something so that you can get CE also... it depends on how much you're willing to change from something that you know works for you.
the only thing I can tell you is that there is no more delay between activating and landing this attack than with an other, it cycles well other attacks, and if you keep auto attack on it doesn't interrupt the attack sequence any more than any other special attack.