Eul's vs. Diffu on support riki

I understand that Diffusal gives great stats on Riki and is often the go to item for him, but recently I've been playing with euls scepter instead. It provides the same utility of removing dust without the limitation of only having a max of 14 charges, gives great movement speed and fixes the mana problem that, at least I, often run into on him. Why do people generally build diffusal and rarely build eul's? Furthermore the cheaper build up is really nice as you can roam with impunity at a much earlier time. You can always go for something like sny or butterfly afterwards if you need extra agi/damage. Just a quick comparison, level 2 diffu costs 3850 and euls costs about 2800, which means you could buy a euls and half a yasha for the same price.