What stopped me load balancing with 4G was the sudden and unexpected latency increases. It would trigger pfSense to mark the gateway as down and the instant traffic stopped flowing the latency went back to normal and it was marked up again, so the firewall would be restarting constantly killing all connectivity.
I tried increasing the latency at which it marks the gateway as down but that didn't help as when 4G was having the latency issue it was barely usable so
needed to be marked as down. It was at that point I ordered the second VDSL line.
I honestly don't know how anyone copes with using 4G as their primary connection. I guess they just get used to the fact some days it will lag.
I believe 5G is supposed to fix this with TDMA? This is also the key feature that should fix WiFi, eventually.