I'm not sure if this question is still open or if I understand the issue. Here is what I have been doing for years - hopefully it will shed light on the question.
I develop my apps on a Windows PC in a browser window using the AI2 development environment. I have the companion app running on an Android phone or tablet for testing/debugging. When my app is complete and ready for installation, I go to "Build | App (save .apk file to my computer)". I use the dialog that pops up to select where on my PC the .apk file is saved (the desktop will do just fine). Next, I plug a USB cable into my PC and into the Android device that I want to install the app on. Windows displays the Android device's storage as if it were an external disk drive. You can navigate through the Android device's file system using Windows explorer, just like any external USB drive.
I simply copy the file from my PC and, using the PC, paste the file somewhere in the Android device's file system. The "downloads" folder will do; however, I usually have an external SD drive plugged into my Android devices so I put the .apk file in the home directory of the SD card. Where you put the .apk file does not matter, as long as you can find it again.
I am then done with the PC and can unplug the USB cable. I use an Android file explorer to navigate to where I pasted the .apk file. Most Android installations come with a file explorer app build in, but you can download one of many free ones from the Google play store if you need to. Anyway, when the .apk file is located, simply tap on it and it will install. On some versions of Android, you will get a message about the file being untrusted and warnings against installing it. The message varies with the Android version, but there is always something that you can tap on that says "install anyway" and the app will then install.
There are other ways to transfer the .apk file from your development PC to your Android device: Google cloud storage, e-mailing it to yourself, etc. But I think that the USB transfer method is by far the simplest and fastest way to do this.