Kudos to Steve for the details in this video, and the subsequent SDG#331, always very detailed.
But I think there is something wrong in its configuration, especially in the final assembly. As you can see from his video SDG#329 the Blue and Brown transformer windings are connected on the PCB in a different sequence:
photo video Steve
On other videos in circulation, however, you can clearly see that the brown pair (70W) should be the one dedicated to heating the tip, but it is connected on the PCB to the input of the rectifier to obtain the power supply for the circuits, while the Blue pair (from 9W) which should be the one dedicated to the power supply is connected to the central terminal, near the power mosfets, therefore clearly inverted.
photos others
This accounts for the dramatic 8 Volt drop that Steve notes in SDG video #331 when he pulls out the handpiece and overloads the 9W Blue coil.
I believe that this station cannot compete with more famous stations on the market with C245 tips, but by connecting it correctly by inverting the outputs from 9W to 70W you should see a big difference and it should work decently. I had the opportunity to try it with c245 and c210 tips and not so bad.
In this other test video, at minute 6:57 and above all with a correct configuration of the transformer output pairs, there are three nice tests with C245, C210 and C115 tips:
https://youtu.be/6h5jQm4XzFk?t=417