Originally Posted by
Mammoth
If you ignore the maths for a second and consider two cases where this glyph will do different things:
1) Everyone taking equal damage -- this glyph performs well because they get a more even distribution of heals.
2) Healing the raid, but one person taking more damage -- this glyph hurts you.
More often than not I'm in the 2nd situation. I click the guy with least health (due to debuff or being the tank) and chain heal from him. Thus I'll go without the glyph. If you think you heal more in situation 1, the glyph is for you.
If you were purely interested in the maths, I think the guy above is correct.