Yeah, I know, you've heard it before. Maybe even been here yourself. But it's true, finding a good featured covert backpack, sling or messenger bag can be frustrating and expensive.
I've tried several of the different big name covert backpacks, unfortunately most are not really covert.

I'm currently using probably the lowest profile backpack so far, but it lacks weapon retention and positioning on the inside.

I'm using an older pacsafe Vibe 20L currently. Low profile, small size, reasonable appearance in urban settings.

With a greyman rmp plate, a single rigid insert, it's limited once I add a mid size pistol and spare mag.

Any one using something else they'd suggest?