So i currently have a rtl-sdr as well and have done testing and it works flawlessly. The screenshots from earlier are form my rtl-sdr. I too cannot afford a hackrf so went the route of rtl-sdr. The biggest thing i saw, I followed the tutorial to the end. Instead of the "kalibrate-hack-rf" you use "kalibrate-rtl" when building kalibrate at the end of the tutorial. Also if you have installed the "kali-linux-all" the "kalibrate-rtl" might be there by default. You can check within the package manager
to see if kalibrate is installed or from terminal type "kal" and see if it runs. if the command "kal" runs you should see something similar to this screenshot below.kal.jpg