Another build with #184.108.40.206 of AutoCAD .NET Addin Wizard 2015 was released. It can be downloaded and purchased from the same page:
In this build, many problems are fixed and issues addressed. The most two important aspects are about side by side installation/run with other wizard products such as Revit .NET Addin Wizard 2015, Inventor .NET Addin Wizard 2015, and Navisworks .NET Addin Wizard 2015, and VSIX (Visual Studio Extension) deployment strategy.
Now two approaches are applied to make sure the extension (having the coders and widgets in toolbars) properly be installed to all application Visual Studios. One is to deploy the extension implicitly in the MSI itself, the other is to double check through launching the VSIX Installer explicitly after the MSI finishes, the final dialog being dismissed.
All in all, the key seems to be with the privilege when running the MSI. Please do run the MSI as Administrator if you want all features to be installed properly. Even if with the Visual Studio itself, running it as Administrator will avoid a lot tricky issues here and there.