The Oregon Open Primary and the California Plurality Top Two differ significantly in terms of intent.
All of the legitimate criticisms of so-called “Top Two” systems are attributable to vote-splitting spoiler effect inequality. This restriction of support for a single candidate in a field of many causes similar candidates to split votes, so if there are an unequal number of candidates representing various viewpoints, the results can be skewed by simple candidate participation. Because all candidates for office appear on a single ballot, this effect is magnified, which enhances the shut out of minor party and independent candidates. Name recognition becomes even more important, so candidates need to raise more money to compete. Plurality with a Top Two compels voters to choose the "lesser evil" candidate on their "side" most beholden to the money.
Because the Oregon Open Primary calls for true equality in the vote, Oregon's 2015 Legislature should necessarily correct this vote-splitting inequality should the measure pass.