There is currently no difference in reload speed when drawing shells from the bandolier as compared to general inventory.
This means that the bandolier is only useful for carrying a few shells at the expense of encumbrance, as opposed to other pockets (ie. ankle ammo pouch, chest rig) which allow for more rapid reloading.
This honestly sounds correct – reloading from a bandolier could even be more cumbersome, as each shell is in a different spot. It’s purely to distribute the weight/bulk of the ammo–and it looks cool as hell! 
More cumbersome than reaching into a bag of scrap metal, lighters, two by fours, batteries, macaroni, arrows, nails, and cocaine?
Ha! More cumbersome than a deliberate ammo pouch, for sure. 
Each individual shell is tucked into a strap, and could be pretty tight, etc.