First of all i got to say this so you don't change it later as you did with press the attack.
* The attack that activates the rune will benefit from the converted true damage but will not benefit from the bonus ad.
* If Illaoi uses W with the attack that activates the rune, the tentacles that attack afterwards won't benefit from the bonus ad but will benefit from the converted true damage. (the same w+tentacle bug happens with phase rush, electrocute and spellthief stacks)
* The damage to the spirit won't be converted to true damage. It looks like it thinks the spirit is not a champion (same thing as black cleaver/bork/tahm/etc...)
PS: If you heal based on physical/magic damage it will feel bad when you activate this rune and start healing less...