If you have a huge tolerance to them already they are definitely not as effective for opiate wd vs using benzos for the first time whilst in opiate withdrawal (aka low tolerance). Thats not to say they are not effective for people with a tolerance though.
I have a mild benzo tolerance and during detox and withdrawl from opiates i found a low benzo dose during the day got rid of the anxiety and even some cravings. Also the fact that I or one would have benzos makes it much easier to smoke weed in opiate withdrawal.
Without it, for some, smoking weed in opiate withdrawal would send them into a panic attack lol... Including myself. Even though when not in withdrawal, clean etc I'm a heavy user of cannabis with no problems in regards to anxiety. If anything it makes it better but not during opiate withdrawal - Its the opposite UNLESS i have benzos. The two together during withdrawal help tremendously.
...Especially with the kicking and restless feeling as well as both possess muscle relaxing properties. I guess this may be why they are both useful for many like myself.
They are also helpful at night as well mixed with a sleep aid. The sleep aid makes you hella drowsy while the benzos will stop the restless body feeling or like bugs are pinching your skin/muscles which makes you unable to stay still (those who have kicked opiates know what I'm talking about but i dont know the name for it.)
My sleep aid of choice is mirtazapine - Trazadone works well too but the drowsy feeling i find doesn't last long enough and therefore doesn't keep one asleep (maybe for some this doesnt apply though - I know for me and others this applies with Trazadone.).
Mirtazapine tolerance does build fast though as the histamine receptors sensitize after some use of mirtazapine.
Mirtazapine also seems to be the sleep aid with the least side effects and least addictive profile. If anything if you look on wikipedia theres a sentence in the pharmacology section which says that it may even be helpful for combatting drug seeking behaviours because of how it works in the brain.
But yeah thats ^ why i choose mirtazapine and why i decide to combine it with the lowest but most effective dose of benzos.
Lets not forget though that benzos are addictive, withdrawal is actually deadly if done wrong, it can be much harder than opiate withdrawal (especially with larger doses of benzos), its worse for your brain (have you see what your memory is like on benzos lol

) and body. And not to mention tolerance builds super duper quick if used regularly. Point here is just use them for the worst part of withdrawal, then don't take benzos again after that if you can...
... For the reasons i mentioned above along with the fact that you would possibly be replacing one addiction with another if you continue using benzos after the worst of withdrawal which is something I doubt you want.
Anyways. Good luck with the detox and staying clean buddy. You can do it.