There are potentially 5 versions for models 81 through 87. The features for each version in models 81, 82, 84 and 85 are consistent between models (i.e., the 81FS, 82FS, 84FS and 85FS all have similar features). This is not the case with models 83, 86, 87 and 89, which were not made in all versions.
Base versions (no letter suffix)
Base versions of models 81 through 87 are noted for having a rounded trigger guard and generally fewer safety features than subsequent versions. Safety is ambidextrous and frame-mounted. The frame is alloy, the slide is blued steel and the standard grips are wood.
The B versions of models 81, 82, 84, and 85 introduced an automatic firing pin safety, a shorter extractor and grooved front and back straps.
The BB versions of models 81, 82, 84 and 85 have more serrations on the slide, white dot and post sights and other subtle changes.
The F versions of models 81, 82, 84 and 85 introduced the "combat" trigger guard with a squared-off front that allows for a finger hold, plastic grips, a proprietary "Bruniton" finish, a chrome-plated barrel and chamber, and replaced the safety with a decocker, which lowers the hammer when operated. As a result, these pistols cannot be "cocked and locked".
Current production models of .32 ACP and .380 ACP Cheetah pistols are in the FS configuration (e.g. 81FS). In models 81, 82, 84 and 85 they include internal improvements over the F versions that are not visible during casual inspection.