Originally I thought Improved Flash Heal was almost mandatory. Back in the day Flash Heal was our workhorse, and so doing anything to improve it was a given.
Later on, after thinking about it and reading a post about the talent, I decided it wasn't so hot. Mana comes a lot easier nowadays, and 10% crit on a spell we don't use as much as we used to isn't that exciting.
But now, I think I have a more balanced view. There are pros and cons to this talent.
- Cheaper Flash Heal. Who doesn't like Flash Heal?
- More crit, when you need it most (low health target).
- More crit also equals more Divine Aegises. Aegisi? Aegooses?
- Only affects Flash Heal. Who casts Flash Heal?
- Mana conservation not that big a deal for Disc priests.
- Crit effect only applies to low health targets.
- Unlike Test of Faith;s steady healing boost, this crit plays a RNG game with a low health target.
The pros may all seem to be heavily qualified by the cons, but let's look at an example situation where this talent shines: General Vezax. For Vezax, you need to conserve every last scrap of mana. And you need to focus on healing a single target, which means you're pretty much just casting shield, penance, and flash (in that priority order). With 3.2's longer Penance cooldown, you'll be casting flashes now and again, so you may as well get them cheaper. And you sure want to keep Inspiration up on the tank, so the extra crit doesn't hurt when it comes into play.
And the real test of any talent is, what else could you be getting with your talent points. In this tier of the Disc tree, you're basically comparing it to Focused Will. This used to be a PvP talent, but it now also increases your crit. Overall, I'd probably recommend going for Focused Will first (I am a crit fiend), but there are enough points to invest in both. At the very least, you can drop one point in Improved Flash Heal: the first point gives slightly more crit than the following points.
An interesting talent choice overall. Not the best talent for Disc priests (though I'm sure Holy would kill for it), but not bad either. And for times when mana may be tight, and single-target healing crucial, it's a solid choice.