That’s kinda what I’ve been reading and my local gun store has been pushing the 507K. Let me ask this, is the HE507k green dot the same footprint?Well, I have zero experience with the Max 9, but a good amount with micro red dots. The Holosun 407K/507K would be my pick for the footprint the Max 9 uses. The Swampfox optics are garbage. Shield dots are expensive and not durable enough for me to want to use on a carry gun. I have seen and had problems with Shield dots. The Holosuns have good battery life, I like having the ability to manually adjust the brightness setting, you do not have to remove and then re-zero the optic to change the battery, they won't cost you an arm and a leg, and I haven't broken a Holosun micro-dot yet.
Hope that helps.