I'm sure the custom fitted MADs work well, but the price on those is on par with a CPAP. The cheaper self fit (moulded after being warmed up in boiling water) are absolutely not a replacement for CPAPs.
In-home sleep studies are cheap now, but in-office ones are even more expensive than the MAD sometimes.
This article is about a guard that connects to your upper and lower teeth, and draws your jaw forward (it has to to help with obstructive apnea). You basically can't talk while wearing, it takes getting used to. They're not always comfortable, but they definitely help. Less invasive than a CPAP, and you don't need a machine/constant power source.
But there's multiple types of apnea, which the paper[0] makes clear (it's only talking about obstructive apnea) - this headline suggests guards are better for all. That's far from true. Obstructive is more common, but; for the other kind (where you forget to breath at night) this does nothing, and a CPAP is the only solution.
[0]: https://www.sciencedirect.com/science/article/pii/S073510972...
I have one of these, my dentist wants me to wear it because apparently I grind my teeth, but turns out I can't wear it. A whole bunch of stuff goes wrong: The thickness means I have nowhere to put my tongue and between that and how it adds volume to my molars my jaw can't close all the way, saliva builds up in front of and below the guard (between the teeth/gums and lips) where I can't do anything to swallow it, and the plastic taste is terrible - the longest I've lasted is about 10 minutes before I have to run to the bathroom and take it out.