What are the issues of running few Direct Access servers (let's say 3-4) per site without External or built-in NLB, please? Aside from manually configuring each server and lack of granular control over how many clients there is on each server, what are other issues, please?
According to https://directaccess.richardhicks.com/f5-big-ip-load-balancer/ there are many:
NLB has some serious drawbacks and limitations and should typically be avoided for most enterprise deployments. NLB is broadcast-based and generates a tremendous amount of noise on the network. Heartbeat messages are broadcast to the subnet every second. As more nodes are added to the cluster, the broadcast traffic grows exponentially. Microsoft suggests a limit of 8 nodes per NLB cluster, practically speaking NLB clusters should be limited to no more than 4 nodes.
In addition, NLB lacks the visibility and granular control of network traffic often required by network administrators. Further, troubleshooting NLB is prohibitively difficult. There are also challenges getting NLB to work correctly in virtual environments, making NLB difficult to support.
