Saw an acquaintance mention the Keppi open collars and tried them out. At around 30 bucks on sale, not too pricey in the first place.
Pros are that it locks the weights in place on the barbell sleeves pretty easily, with either one or two of the clasps making it tight (probably should use both for safety). Also, it's magnetic so I store them on my rack's uprights easily as well.
Con: clasps can be kind of hard to remove, tweaked my fingers a couple times before figuring out how to do it carefully and not get hurt.
Are they as good as the Eleiko Oppen collars? Probably not, but for a fraction of the price, it's hard to beat.