What kind of jars are you inoculating? If you are doing BRF jars then I think it isn't absolutely necessary, but good practice anyway. My experience with it is fairly limited, but I can say the 30 jars I've done with BRF I didn't use a glovebox and have 0 contams. The last set I didn't even clean the room like I did for the previous sets and didn't have any problems. All I did was wear gloves, a dust mask, and flame sterilizer the needle between jars with an alcohol lamp made from a baby food jar and a piece of heavy twine. This is just a hunch, I have no evidence to support it, but I think a good portion of contams come from improper sterilization of the jars.
The more I've been getting involved in mycology I've considered using one at some point for future experiments. If I start having problems I'll definitely start using one, but until then it's something I'm probably going to put off. Not that they are expensive or difficult to make, just that they are bulky unitaskers that take up a lot of space.
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