I have 6 Galaxy Turrets fully upgraded but they seem weaker than my Zakanas and im gonna upgrade them to Zakana G
One weak point about Galaxy is shielded enemies, because it back the bullets damaging my Tytan Barriers.
The strong point about Zakana is the Shield Disruptor upgrade.
Are Fira Zevon worth upgrading them?
You should definitely use Zakana Gs; Galaxy Turrets and Fira Zevons have lower DPS than the Zakana (and will never catch up to its DPS since they all have amplifiers), lack both Team Vigor and Shield Disruptor, which are amazing support upgrades, and have reflectable shots, which is a major nuisance in PvE and a huge disadvantage in PvE. In addition, the Fira Zevon's explosion isn't very effective, especially on a low-damage turret, so they're not really worth upgrading.
What level do they upgrade now. Some of my units are at VII but I don't know how to upgrade them or when I am allowed.
Sorry I'm 9 days late but when you get the amount of gold needed to upgrade the unit, the button will appear. The amount of gold can be anywhere from like 500 to 100,000, but most turrets should be around 25,000 or under.