My husband is not the usual ALS patient, but I'll add his experience with Botox. He has been having Botox injections in his salivary glands for about 5 years now to keep him from drooling or choking and getting the saliva into his lungs. He has one injection on each side just under the jaw bone and another one on each side near the side burn area for a total of 4 in all. He started out every 3 months, later went to 4 and now does every 5 months. He says they are not painful and doesn't even flinch. He has also never had any side effects that I am aware of. He does get really dry eyes which I think is a side effect, but the doctor doesn't.
Although he has done so well, the doctor went over the risk with him and left the decision completely up to him. He told Rick that since he can't see exactly where the gland is, if he misses just a little and hits the muscle instead, it will cause the muscle to work even less, sag, etc. This will cause even more problems than he presently has. Rick still wanted the procedure.
His doctor is apparently one of the best. He gets the injections at the VA, so cost has not been a factor.