I agree that he should try everything else first. But if he is at that point where he is ready to tie the noose and go ahead with finishing himself, then he needs something that with calm him down ASAP........and benzos may be the only thing that does that.
ALTHOUGH I would advise on trying his amitriptyline or mirtazapine first.....those can have a very strong drowsy effect and I have found that that also helps one to calm down somewhat (I am on mirtazapine myself).......it's hard to be real panicky and angsty while being knocked out to the point, where all you can think about is sleeping.
I agree that mirtazapine is a much better option to try out first. If he has to take Benzodiazepines he needs to be aware that this is supposed to be taken during very short periods, the main issue is that because they do have a beneficial effect, short term, on the perceiveness of tinnitus, he may be tempted to start using Benzodiazepines chronically/more often, and he may start to build a tolerance and addiction very fast (Benzos are very addictive, some become hooked after less than a week at 0.5mg... when I said it's more addictive than Opioids, I don't exaggerate things).
While tinnitus will improve in the short term, this will only work until the tolerance builds up so high that the drug no longer holds any positive effect (depending on the dosage it can take a few years to reach that point), then the nightmare begins, as he will be forced to withdraw and it's the very harsh withdrawal symptoms that will get you, they do possibly (and likely) include (much) increased tinnitus perceiveness and new tinnitus noises which can last months AFTER being off the drug, which itself can take years of slowly tapering it off.
I shall add that Benzodiazepines is one of the few drugs for which withdrawal symptoms can be fatal (yes, you read that right, they can outright kill you, especially if you "cold turkey" after chronic use), that should give you a somewhat acute representation of the severity of these symptoms (which, shall I remind you, can last years), the faster you stop Benzodiazepines, the more severe the symptoms will be.
Benzodiazepines do have their uses, especially against depression, but they must only be used for a very short period and under strict supervision, unfortunately many (most) medical professionals are very keen on prescribing all kinds of pills for all kinds of ailments, most often irresponsibly, regardless of their long term side effects.
"Having some back pain? No problem! Take this Oxycodone pill!"
"Having too much Cholesterol? Here's some Statin!"