You don’t have to go TB3/4, you could go USB3-C and save a bit. If/when I redo my design I’m gonna try it in OpenSCAD so it’s a bit easier to be parametric for easier end-user adjustments. The big advantage to getting a dock is if you have multiple devices it’s really easy to switch things around at your desk without much hassle/readjustment. Always the same desk/monitors/keyboard/mouse between my personal laptop and work laptop while working from home.
As for the differences, I went hinge down because of the design XPS 13, and stability, what I had when I originally made it. It works for my XPS 15 well still, but my work Latitude 7390 does struggle a bit with the layout. I also just feel like a lot of the weight of my laptops are towards the hinge and feel safer having that lower center of gravity. I have thought about putting some cut-outs where the cable cubby is to provide some airflow paths for the redo. I also do have a dust filter on the air inlet side of the fan. I like the clamp-to-hang idea, reduce the footprint in a round about way by getting off the available space.