Yes I know Lothar Schanne who made those tests. I think the Neumann panels work well for high resolution spectroscopy within a limited wavelength range, particularly H alpha with the LHIRES III spectrograph which was what Lothar was doing there. For that particular application they worked better than the usual halogen lamp, matching the defects caused by dust for example. Note that some panels from different manufacturers have some sharp emission lines which make them no good for spectroscopic flats.
I don’t think they work as low resolution wide wavelength range flats (for the ALPY or LISA etc) though as they have a limited wavelength range with no output at the UV and IR ends compared with a halogen lamp. (Francois Cochard commented about this at the recent workshop)
I have a small one knocking about somewhere. I will see if I can dig it out and test it with the ALPY