As a lvl 50 SCH (and lvl 34 WHM), I've been running nearly all the lvl 50 instances and its going fine.

SCH advantages:
1. Has shields
2. Doesn't going oom (easy)
3. Cool pet buff (spell/skill haste, healing potency/resistance/aoe buff stuff)
4. Instant 20% healing spell, which you can spam at most 3x per minute (takes practice, but saved many asses).

However what I regret not having from WHM stufff are:
1. Aoe medica heals for pure heals.
2. Not having a cure 2, which is more powerful (but less mana efficient).
3. Somehow WHMs can resurrect people with no death penalty.
4. The panic 100% heal thingy (Instead the SCH 20% heal spam thing compensates though in a way, cuz u can u use it more often).

I would still prefer playing a SCH anytime, since ur kind of an underdog. And you have a higher chance of getting another WHM to combine the strengths of both healer types.