Putting aside that one of my favorite RPG memories is strolling into a vampire nest in Baldur's Gate 2 and watching my avatar turn Amn's greatest threats into ash just by looking at them... I still find this feat badly underpowered.
Brief history lesson: channel energy in PF1e "replaced" D&D's Turn Undead, but it did include a feat that let you spend a channel to achieve a similar effect: causing undead to flee for a minute, with intelligent undead getting a new save each round.
In the playtest version of Turn Undead, there's only an effect when undead *critically* fail their save against Heal or when the cleric scores a crit on the touch attack (neither particularly likely given the well-documented power of monsters in the playtest), and that effect being a paltry one round of fleeing.
In short: it will be very rare when this helps (maybe tops 15% of castings of a specific spell on a specific enemy type; and a spell largely meant for allies most of the time), and its help won't last. *Not* a good choice for a feat
My personal suggestions:
1) Just bake this effect into the heal spell as is. With such a low frequency, this shouldn't upset the experience. (though, I will admit, thematically doesn't quite fit if it's an occult or primal casting of heal)
2) Make the feat take effect on a failure, instead of a crit failure, and possibly extend the duration as well to 1 round/player level. (With the extra saves for intelligent undead)
3) Maybe even combine suggestions 1 & 2
4) Have the feat grant a spell power comparable to PF1e's Turn Undead feat. No damage, but decent odds to send undead running for a meaningful amount of time.
I'm curious what others' ideas are. Did turn undead need a nerf, and I'm just a bad GM for not realizing it?
Basically Paizo nerfed all kinds of save or suck. If it can cause the target to lose its next turn, it probably only works on a critically failed save. Since heal is a 1st level area of effect spell, fleeing for 1 round on a failed save would make it quite overpowered compared to other low-level spells.
Sadly restricting this feat to only work on critically failed saves makes it almost useless. The only time you're ever likely to trigger critically failed saves is when using the area of effect version against large numbers of weak undead, but is it really worth investing a feat for something that basically works in one narrow situation that you're already well-suited to address? I don't think so.
Personally I think Paizo needs to take another look at save-or-suck. I think they've overshot the sweet spot. It was a bit too swingy in PF1 where it only took one failed save to completely screw you over, but now it feels like it's so inconsistent it's not even worth attempting.