Rigid fiberglass is bonded with resin and won't become airborne unless it has been disturbed and there's nothing covering it- Rock Wool can be an irritant, too. If you don't know what an MSDS (Material Safety Data Sheet) is, read this.-
http://www.americanrockwool.com/_docs/rwpp/RockWool Premium Plus SDS.pdf
The materials needed depend on the effect needed and the only real way to know this is to measure the room's acoustical characteristics- this isn't done by professionals using guesswork. Any material will have certain abilities to block, absorb, reflect or diffuse sound and they have been measured- it's the only way for someone to recommend something as a remedy to an acoustical problem. If you look at the specs for different materials, you'll see NRC (Noise Reduction Coefficient),STC (Sound Transmission Coefficient) & other acronyms and they come with graphs to show their effect at specific frequencies but mainly, they're used for frequencies above the low end because that range is harder to absorb- they'll often prefer to isolate the object that causes the noise, to stop structure-borne transmission. When you look at the graphs, you'll see that their effectiveness falls off as the frequency drops- many are almost useless at frequencies below 150Hz.
There are three ways sound can be transmitted; direct radiation from the source to the listener/mic through the air, structure-borne and modulation, which means that something is made to vibrate and re-radiate the sound- the last two are likely the cause of problems like the one in the thread about the projection screen that rattles.
This leads me to the question- what problems with the sound make you believe you need to treat the room? If you hear fast echo from percussive sounds or you hear sounds that seem to come from the left of the left speaker or the right of the right speaker, the rock wool in the walls won't help. If you hear the drywall 'ring' (vibrate with a specific frequency) from certain notes or you have problems with sound passing through walls and ceiling, it will help.
You don't need millions of dollars of test equipment- a laptop with a decent mic and a program like RoomEQ Wizard will tell you a lot. You can also find out how reflective the room is with a smart phone and an app like ClapIR but first, I would recommend reading about sound control- there's more info than anyone would want to read but having a good foundation in this makes the solution easier to find.
BTW- I'm not saying the rock wool is useless, but again, the actual problem and problem frequencies need to be known. I measured a room and found that it had a bad problem with cancellation around 80Hz and a smaller one at around 150Hz. Normally, this is caused by reflections from more than one surface that meet in places where the energy from one cancels the energy from another, so I made some panels and found that they didn't make much difference. Out of frustration, I gave the side wall a moderate thump with my fist and found the problem- it hadn't been insulated, as intended. I went to the backside of the wall and loosened the drywall to look inside- empty. We told the homeowner to have his guys insulate it and when we went back, the problem was gone and that wall was as dead as the other walls and the ceiling. Ironically, the homeowner owns an insulation supply/installation company. The outer surfaces of the walls and ceiling have no treatments- the floor is carpeted and the corners where the walls and ceiling meet have a small, angled soffit, with a larger vertical column that's similar at each side of the screen, which frame the screen and contain the L & R main speakers and the subwoofers below them.
