I know that opinions of the merits of ArmorAll, based on experience with its use, are highly polarized. I wonder why.
I paint it on with a cotton swab, then set the bins in an open clean area with good air circulation for 24 hours or so, then wipe away any excess with a fine lint-free cloth. I'm left with rubber parts that are clean, dry to the touch, and not especially slippery (sure, I know excess ArmorAll can make things slippery. Some people spray metal poles with ArmorAll or silicone spray to keep squirrels from being able to climb them to reach bird feeders). I've never dropped a bin, and certainly never thought that ArmorAll use raised the risk of such. I've treated all my bins like this since ~1993, and none has experienced any of the deterioration of eyecups or armor that I saw before I started doing this, and that I still routinely see in my friends' bins who don't follow this approach. So I'm very happy with the results. I also note that when I've returned bins to Leica and Zeiss for mechanical repairs that they've applied ArmorAll or something equivalent before shipping the bins back to me.
I live in a very humid climate, and my bins were kept for many years (before I could afford AC), or decades in some cases of those passed on to me from others, in conditions of high summer heat and very high humidity. Photographic negatives and slides in this environment have to be stored in very clean conditions to prevent fungus from eating their gelatin emulsion. Likewise, I'm vigilant about keeping lenses clean to reduce opportunities for fungus. Unless they can be stored in climate controlled places (houses with AC, or dehumidifiers), leather cases and coverings (on old bins) need regular treatment to prevent them from turning green with mold, as happens with leather-bound books. But I've never found/thought that humidity had any relevance to the preservation of rubber/fake leather/synthetic parts.
--AP