Thanks for playing the full demo!
The demo is intended to last around 20-30 minutes. Normally, you wouldn't max out an upgrade before getting 1-3 layers above it, which is why it feels slow after the 20-minute mark. It's very important that the feedback you've given, I will start looking into a way to implement a proper condition for informing the players that they have finished the Demo.
In the next 50th version update, a minimal clanker spawn of 3 small blue ones will be added.
In the current version, dragging is added to the skill tree, as many people mentioned that the old movement was unintuitive.
A weapon slot upgrade exitst, and is available in the later stages of the game, which are unavailable in the Demo sowy.
Thank you for your feedback, its very constructive and helped me a lot in building a list of fixes the game needs.
Have a prosperous day!
Leon.D :D