End user here, not Greenbay, but: I don't think D-Link can ever officially describe a beta as "safe", after all it wouldn't be a beta if they had tested it. But as an end user I can confirm both 1.04.01 and 1.04.04 are far more solid than 1.03.04
One thing: for some reason the transition between shipped firmware and 1.03.04 ends up messing up the configuration, so I personally recommend doing a factory reset and reconfiguring (don't restore from a back-up.) I know it's a pain if you've made quite a few adjustments, but it's worth doing, and only apparently needs to be done once.
I am not having any issues with Wi-Fi stability or disconnection issues with the current firmware but did with 1.03.04. So hopefully it'll fix your issues.