There are several problems with this approach:
- The package will never get updated
- The package manager won’t know about it, this may cause it to be installed more than once, block updates or block the the installation of other packages
- The libraries those binaries expect to see may not be installed on your system
- That process ignores dependencies
If you really, really need to install a deb or rpm on your system, the best approach is to create PKGBUILD for it.
You should also avoid using debtap.