Have shot several, know a few dozen with one and have never heard anything bad about them even once.
It is basically like Aimpoint just kept making their older model, and pass the savings on to you with lower cost components and working out the manufacturing details. More or less. It's not the latest and greatest Aimpoint, but those are over $800! Comp M4s (they are up to M5) go for over $500 /used/ and in not great condition! The PRO is a steal.
Because it is not made in Bangladesh with their name but IS full Aimpoint quality, made in the same factory in Sweden, broadly the same as the best they made 10 years ago, so a hell of a nice optic. When people get invited to do factory tours and make a sight, they often do PROs. It's a hell of a factory. Here's Larry Vickers videoing his tour
If you like Aimpoints (my eyes suck and hate most red dots, so I only have a couple) and do not jump out of airplanes to land in the water then dive to attack enemy ninja bases, the PRO is absolutely to be suggested without any reservation. And... even then it might work. Here's a PRO that survived a house fire:
https://www.outdoorhub.com/news/201...ts-aimpoint-red-dot-that-survived-house-fire/
Compared to the Vortex, the smaller dot should also make you happy.
If it didn't come with instructions or you don't read, the QD mount is fine, but just use it carefully to make sure it's secure, aligned, and re-zeroes if you have to pull it off. Again, slightly old-school, so it works but is not the sexiest. Make sure the mount base and rail are clean; not scrupulously, just no dust, debris, leaves, cat fur, etc. Normal clean. Mount the thing, then turn the knob. Once you get resistance, turn it past that till it clicks TWICE. You can do once or three times, but twice is the sort of standard, and if you do twice always, it'll mount the same, always.
P.S. For anyone else who hasn't bought yet, the ACO is a notable step down in several ways, and usually within like $30, so spend the extra for the PRO.