We've had some issues with the firmware.
The solution is quite advanced. You need a lot of training to use it effectively.
When we bought the equipment, and we have more Juniper devices, not just SRX, they started to malfunction. I'm not sure why. All the devices that we bought were from the year 2018. We had the EX4600. Something was not working with this device. It was offline. We bought everything in twos so we could make a high availability with all of them. The current has malfunctioned, and all the warranties have also expired. We are, generally, expecting malfunctioning, maybe in the next few years. I was planning to switch the Juniper equipment with something else to avoid this.
It does not have a simple user interface.
The warranty offered on the devices isn't long enough. it would be better if you could extend it out to five or eight years. Otherwise, you have to be very careful with the equipment.
I'm not sure if Juniper SRX can filter emails or block viruses. I'm not familiar with these aspects as I haven't had that much experience using the SRX inside the UI. However, if they do not, it would be ideal if they did. I'm not sure if it can deflect any kind of DDoS attack.
The one particular issue that I've seen on the SRX, is if you have SSH enabled and if there is a large number of SSH connections, when a brute force attack happens, the SRX, in general, tends to become unstable, or it resets by itself. That's one issue that's particularly making me angry, and I had to request the reseller to block the SSH permanently, or just to allow access, so only they can connect.