Since all my active machines already have berrybrew installed in my unique manner, and I didn't want to mess up the workflow on those, I created a new Win10 virtual machine (1809, 17763.379), and tried downloading your link. The first few times, MS Edge / Windows Defender flagged the installer as containing a virus; I installed chrome so I could download, and successfully installed it; when I tried to re-download with Edge again, or scan the berrybrewInstaller.exe with Defender, it didn't flag it as a virus this time. (So sorry, I don't have a record of which virus it thought it was.) Even after I reverted to my pre-installation snapshot, it wouldn't flag as a virus again; so sorry, I cannot tell you what virus it thought it was.

As far as the actual process went: when I first ran berrybrewInstaller.exe, UAC asked to make changes, but other than that, it worked as you described. The uinst.exe did what you expected, as did re-installing. If i tried running berrybrewInstaller.exe after berrybrew was already installed, it asks if I want to try to disable it (I assume that's the new fix for 1.28 vs 1.27 that you made in response to swl's input). If I say no, it aborts; if I say yes, it moves forward, warns me about off/config/switch, then installs overtop the old (since it was in the same location). Looks reasonable to me.