As Thomas said, this product is an upgrade to OS3.1.4, not 3.9, for many reasons. We'll supply a rather lengthy FAQ, which will also cover that topic, so I won't go into detail here.
But I'd like to emphasize one thing: You can spend all day to discuss whether this thing is worth the trouble, waste of time and energy, complain about things OS3.9 did better 18 years ago, etc.. Or not.
What you'll get is what's possible under the circumstances. There has been no alternative, no "better", "future-proof" approach. Lot's of "DOs": We couldn't do more. It was either do or don't. Maybe someone could have done better, but he did not. Let's leave it at that.

So, now you have another *option* to build your own system, nothing more. The glass is half full - why not have a sip? You may even like the taste.