Heal is fun on Tristana, but Bloody and the whole arsenal of AD is more than enough- Heal does help boost her survivability, but from early to mid game im super fed off of minions and basically i can lifesteal better and faster than the typical healing spell...

Crit is okay, but i prefer raw damage because its cheaper to buy- I kicked a fed cait and vayne's *** when they tried going crit ad, but again how you play is how you play.

I'd add something to the build to give is more crit chance and might consider heal as summoner spell in case you jump someone and you need some extra life to not die.