We cannot secure a specific IP class with this firewall.

Another loophole with Hillstone T-Series is that when we connect through WiFi and turn our hot spot on, all who connect through the hotspot get all the functions, and the security does not work.

Whatever improvements I wanted, they put on the A-Series. The new A-Series recently launched a few months ago. It has all the bells and whistles, so I can't complain anymore. 

Although Hillstone T-Series has a good technical support team, the communication issues could be improved.

The initial setup is a little bit more complex.