I think this may be a bit too potent, and not unique enough. Generally, just combining two trees doesn’t give a great result. Specifically, it’s too similar to Death Watch Warrior with the jetpack talents, meaning that there’s no reason to take both. Likewise, most specialization trees, and universal trees in particular, should have a talent that is unique to them.
Also, with the exception of Supreme Armor Master, once you remove the Death Watch Warrior talents it’s pretty similar to a couple existing trees. If someone wants to be a Mandalorian armorer, they could pretty easily get Gadgeteer and then Modder or Outlaw Tech (probably Outlaw Tech), or maybe Outlaw Tech and Death Watch Warrior. Either would achieve roughly the same result, and they’d only lose out on Supreme Armor Master.
My suggestion would be to pick a different secondary niche for Forgemaster, or just not make the tree, pointing interested players to the combinations listed above.
As it stands, there is not much about the tree that actually requires the characters to be mechanically oriented. Both Inventors and both Gearheads are entirely optional, and the rest are either passives (Tinkerer, Jury Rigged) or unrelated to mechanics. This makes it a good tree for any character to pick up, and outright better than Death Watch Warrior since it has all the same special talents, plus Tinkerer, Jury Rigged, and Supreme Armor Master.
Specific points regarding how the tree is currently constructed:
Inventor is too cheap. The only time it appears below tier 3 is in the Armorer tree. With a second rank then added in a cheap position, it becomes very easy to stack Inventor Boosts when combined with Outlaw Tech.
Gearhead is too close together.
There’s a typo in Gearhead where it should say “halve” but it says “have.”