Full cone NAT on ISP modem problems

[PLAY3R]

Hey all

I have looked and looked, but can't find the answer.

My ISPs modem (Bell Aliant) has a Full Cone NAT option, and with it being off, some apps on our phones and our Alexa devices do not work or work very Intermittently.

With Full Cone NAT turned on and the pfSense IP in a DMZ. Everything works.

My question is. Is this a good setup, security wise?

Thanks!!

PS: My ISP modem does not respond to WAN pings. If that matters