This is extremely unlikely to be an existential risk, and working with such viruses helps a lot to understanding how to combat similar viruses. It is very important that they be very careful that they don't get out of the lab, but the level of precautions generally taken for this sort of thing is extremely high.
The important thing about this research is that it shifts our estimate of the likelihood of H5N1 human-to-human transmission upward (for all intents and purposes, ferrets can be considered little humans when talking about flu). Some previous research (theoretical, not experimental) indicated that it was nearly impossible for this to occur, requiring multiple "high energy" (i.e. low-probability) mutations. These guys seem to have done it relatively easily, which is pretty horrifying.
It is indeed unlikely that the particular virus bred by the Dutch...
I'm woefully underinformed on this topic, but this doesn't seem good at all:
I feel as though I ought provide more commentary instead of just an article dump, but I feel more strongly than that that what I have to say would be obvious or stupid or both, so.