MSMA (monosodium methanearsonate) is an arsenic-based grass killer. It kills grassy weeds such as crabgrass and goosegrass without harming most turfgrasses. It contains organic arsenic that, according to the University of Tennessee Extension, is less harmful than aspirin.
There are several styles of hearing aids available, from the smallest - Invisible in the Canal (IIC) to the largest and strongest - Power Behind the Ear (BTE), and the very popular Receiver in the Canal (RIC) - made to fit most hearing losses while remaining nearly unseen.
A lot of people with this question spend valuable time agonizing of which hearing aids are best and therefore which to trial. It's important to understand that all major hearing aid brands are of equivalent high quality (Phonak, Oticon, ReSound, Starkey, Widex, Siemens & Miracle-Ear, etc).