The life-support-belt "halos" were an animation shortcut so that stock character cels could be used without the time and expense of having to draw and animate spacesuits.
These for me fall into a category that I'm not sure what to call. Probably TV Tropes has a name for it that's a lot pithier than "plot-solving free miracle tech". Science fiction shows can easily fall into the trap of creating a gizmo for a specific script that has a negative credibility implication for the series as a whole.
"If they have this, why don't they keep using it? Why didn't they use it back when x, y, and z happened? Why isn't it standard procedure?" A great example is the subcutaneous transponders in Patterns of Force. Why on earth not make those part of the SOP for all landing parties?
Writers that are good at thinking through their plot give things like this an in-story reason why they were only used once. An obvious drawback or cost. A hard-to-replace object that gets depleted. A consequence that only becomes apparent after that one use. A sacrifice paid to make it work. Otherwise the main characters just look like morons for not equipping themselves on every mission with emergency recall transponders that can't be stolen by the natives, and magic life-support-halo belts that save them from all manner of hazards. Oh yeah, and of course a few doses of kironide from Platonius!
Brad Wright's writing team seemed to put a lot of thought into the limitations of their miracle tech. In the Stargate franchise, the gates (whose features are partly from the movie and partly from Wright's team) can teleport you to countless other planets in our galaxy (and a couple of others), but they can only travel in one direction at a time, don't guarantee you can come back, can't be kept open for more than 38 minutes, require a unique access code for every destination, etc. These limitations aid the suspension of disbelief, and create plenty of room for things to go wrong and for clever plots to unfold.
Also impressive to me is the list of restrictions on the time travel model used in the Netflix series Travelers: you can only go backward in time so it's always a one-way trip; you have to have precise four-dimensional coordinates (time, elevation, latitude, longitude); you can't ever go back any farther than the latest jump, so no undoing your mistakes before they happened; you have to do extensive research first, because every jump is guaranteed to impact the timeline by the very nature of how it works; repeated jumps to or from the same person take a physical/mental toll; and so on. That was an exceptionally smart show, and the care they put into limitations really paid off dramatically.
So anyway, that was a long-winded way to say I'm glad that Star Trek forgot it had the life-support halo. It's one of those magic tech gizmos that just isn't dramatically sustainable. It solves way too many problems with no apparent cost or other downside.
