Who ever told you that has no idea what they are talking about. Debian testing is more stable than the average release of other distros.
Debian is great in general but the wonkyness surrounding the freeze period gave me the impression that Debian Testing really is something that should only be used if you are interested in helping Debian produce the next Debian Stable release. Some packages don't get timely updates and are only updated close to the freeze period, in preparation for the next stable release. And during the freeze period itself everything is super awkward because preparing the next stable release takes priority over keeping Debian Testing usable.