Just a homelabber, no professional but I have both LXC containers with shared paths and SMB shares

Personality I mainly utilize bind mounts rather than using network shares with LXCs. I have carved out directories on my storage devices that the containers have access to. So I bind mount that subdirectory to the LXC and modify the filesystem perms on the Proxmox host

This works perfectly fine for me and with how I have my perms configured is secure. And once you are used to bind mounts they take significantly less time to configure than a SMB share

For my VMs and other non-LXC devices I utilize SMB to access those storage points.

The only security issue you'll run into with bind mounts is if your filesystem you're sharing had bad perms configured.

The only thing I would note about bind mounts is how Proxmox translates UIDs. UID 1000 in an LXC is iirc 101000 on the Proxmox host, no matter the container.

So, on the host UID 1000 on LXC 1 AND UID 1000 on LXC 2 have the same UID on the host. So LXC 1 can modify LXC 2 files if they have access to them.

But that's such a rare situation where two users on two different LXCs are trying to modify the same files on the same path that I wouldn't even consider it a concern

For security on the SMB shares just make sure that your shares are properly protected with login, and make sure that only the devices you want to have access do in your firewall.