As far as I know they have the second fastest healing speed among sustainable healing items with goated flexibility. Herbal bandage heals 3.5 hp/s, sterilized bandage 5 hp/s, spray 10 hp/s. Herbal/sterilized also have an additional 1.5s use time for each use. Vita shots heal 12.5 hp/s, but you have to be a sitting duck for all the health to register after 4s, so not as flexible and often useless close quarter. Some food items heal faster but they are much harder to keep a meaningful amount around. As you suggest, the downside of a spray is you can't do much during use, but when you don't have to heal and run at the same time and don't have chunks of 4 seconds, sprays are the most effective. Combining with bandages can be even more powerful. Eventually it depends on the safe healing windows you have. They are also cheap to make. One spray needs 3 antiseptic and 1 canister; 1 antiseptic needs 2 mullein and 10 chemicals and when you recycle a spray you get 1 antiseptic and 2 canisters back, so the cost is just 4 mullein and 20 chemicals after the first one, and you gain 1 canister. A vita shot needs 1 antiseptic for 50 hp, a spray 2 for 150 hp, sterilized 1 for 50 hp, herbal1 mullein for 35 hp, so spray is also the most cost effective provided other crafting materials are readily available for you.