The problem is not with the Neo materials that have been in use in speakers for the past 20 or so years, it was with the early experimental grades that were not suitable for applications such as motors (speaker drivers are in effect a form of linear motor). The solution was to develop appropriate grades for motor applications (and the temperatures that exist in such appliaction) and not more efficient cabinet designs.
The reason I feel the need to dispell such myths (it's a myth because it's a false belief based on an inaccurate understanding of the topic that is perpetuated by folks who continue to misunderstand it) is because I probably address this topic pretty often. The Curie point of the grades of Neo used in speaker magnet systems is probably over 300 degrees F, and when measuring the magnetic material temperature (the magnetic slug is not right next to the V.C. but buried between the return casting and the top plate/pole piece) is going to be somewhere between 120 and 150 degrees F when the speaker is operated at ~ the RMS rating or thermal limits of the speaker, and for bass applications the mechanical limits will be reached at roughly 25% of the thermal limits in the worst case crest factor application.
Regarding brittleness, the ferrite materials are at least as brittle and worse, they are externally exposed to damage. The neo slug is totally protected in a speaker application.
Corrosion is handled by various methods such as zinc plating, chromating (no longer common due to hex chrome issues), passivation, powder coating, painting, etc. It's not a problem except in the cheapest of speakers... not speakers that any of us in the bass amp industry would even consider using.
