I cannot attest to the sound from Bluetooth Speakers in the helmet. I have never tired that.
I have used, in the distant past, regular speakers in my helmet from a good source with reported good sound quality (I had no way of personally measuring the quality).
Issues. In the helmet speakers for audio (music, audio books) are suppressed by the wind noise from riding. Even a quiet helmet will generate wind noise at speed. The way to reduce that wind noise is, for some, to wear ear plugs that reduce the sound level. It might work. Some say it does.
In the ear speakers with molded earplugs that fit your ear not only provide noise reduction, they also can provide high quality audio.
I have used the non molded in the ear speakers (ear phones) and they are ok but just OK. And yes they are less expensive than the other route.
The route I chose about 7 years ago was to use a product from Ear Inc. Their current version is different form the original version I started using years back. (see link for item).
https://earinc.com/product/iplugz-pro-sports-earphones-gen-i/It requires that you go to a local audiologist and get an ear impression made. Then you ship that impression off to Ear Inc to get your molded in the ear speakers. And yes there is a cost involved.
The plus side is that they can be worn all day with no issues in fact I don't like to take them out when I stop because it means I have to put them back in. I forget they are there most of the time.
The audio quality is excellent.
Down side, as I said the cost and the wire.
Many folks will say they get by with just the ear buds you press in your ear and those might work but I found they tended to come out if not inserted exactly right and provide little if any noise reduction.
Regarding Bluetooth in general. My audio system on my bike is wired. I guess I could switch to bluetooth but they I have to worry about pairing, losing pairing, having my wife paired to the same source, pairing any microphones for speaking, you get the picture.
On the Valk, I have just one wire for each of us which combines the audio from the GPS and the radar detector. No mics.
On the wing, same thing, one wire ties our helmets to the Autocom audio system which combines in the wing's audio, the GPS, and the radar detector. A wire then connects the earphones to the helmet lead in and we have good audio for communication and listening.
