I played through the tiers in the alpha (Tiers 0 - 3) and I really enjoyed the progression throughout the process, however there were two things that really stood out to me and made the game significantly easier.
Some of these have been brought up before as separate things, but I think they are more similar and the same problem.
1) Handcrafting speed is extremely too fast, with a 250% boosted reinforced iron assembler, it takes 6 seconds to make ONE. Using the handcrafting bench, I was able to make TWO reinforced iron in ~6 seconds. When trying to unlock new researches, there is almost no reason to even build a factory through at least the first 4 tiers.
2) Building a factory is core to the game, and should be a requirement for success and advancing tiers. Obviously items like reinforced iron are essential to making Constructors and Assemblers, therefore they cannot be removed from the crafting bench as the game currently stands.
However, items like medical inhaler (requires 4 items of input for full healing), rotor (screws and iron rod), modular frames (reinforced iron and iron rod), and potential late game items (steel, aluminum, etc) should all REQUIRE an assembler to manufacture. Removing these items from the crafting bench would force the player to design a factory to produce these items for progression (space elevator for new tiers, etc).
With these two changes, I think the early game could be expanded in time required to progress, without discouraging players unjustly.
Thanks for a great 3D factory building game!