I've done some playing around with his. I've found that using flash of light to stack the buff, there are ten seconds left when the fifth stack is applied, meaning that the full +100 stack will last for 20 seconds (10 seconds until the buff fades and then 10 seconds more). This means that each time I apply this, the healing bonus on my target will be:
+20 for 1.5 seconds
+40 for 1.5 seconds
+60 for 1.5 seconds
+80 for 1.5 seconds
+100 for 20 seconds
0 for the remaining 94 seconds out of every 2 minutes.
This works out to an average of +19.16 to healing, per person. If I wasn't using this I'd be using my trinket that gives +70 healing just to me, so in order for the ribbon to be worth it there needs to be 4 or more healers also healing my target (4x19.16 = 76.64 total bonus healing).
Once this item gets upgraded in the patch, in addition to the MP5, the fact that it gives +30 healing per application will raise its average healing bonus to +28.75, meaning there needs to be only 3 healers on a target to make it more useful than a standard +70 healing trinket.
+20 for 1.5 seconds
+40 for 1.5 seconds
+60 for 1.5 seconds
+80 for 1.5 seconds
+100 for 20 seconds
0 for the remaining 94 seconds out of every 2 minutes.
This works out to an average of +19.16 to healing, per person. If I wasn't using this I'd be using my trinket that gives +70 healing just to me, so in order for the ribbon to be worth it there needs to be 4 or more healers also healing my target (4x19.16 = 76.64 total bonus healing).
Once this item gets upgraded in the patch, in addition to the MP5, the fact that it gives +30 healing per application will raise its average healing bonus to +28.75, meaning there needs to be only 3 healers on a target to make it more useful than a standard +70 healing trinket.