This has probably been posted elsewhere, but I was doing a little testing on the Seal of Insight/Multistrike relationship just for kicks. To help you understand what I'm saying below, you must understand that MS has two interactions with each SoI auto-attack because it works with damage and healing.
-The first MS interaction is the attack that triggers the SoI heal. While the primary attack does, multistrike attacks do not trigger the SoI heal. You will only receive the SoI heal for the primary attack.
-The second MS interaction is on the heal triggered by SoI. When you attack a target and trigger the SoI heal, the heal itself can multistrike and heal for 16% of spell power (32% on critical) as well as an additional 30% of the SoI heal amount (60% on critical) two times. In my current gear with Blessing of Kings, a single auto-attack with SoI multistrike critical procs can heal me for 5778 HP (SoI crit heal (2626) + MS SoI crit heal (1576) + MS SoI crit heal (1576).
I'm not terribly sure who this information could be valuable to, but I was just curious and wanted to find out for myself. As you already know, the heal amount provided by SoI is rather nominal, but it never hurts. No one cares, but now you know. I'd also like to say "Hi" after my two year hiatus from MMO-Champion.
P.S: I need to update my signature image now.