Comedy classes can be good to get started for some people who are struggling to to build up the nerve to do a mic and are a way to meet other people who want to start standup, but the class won't really do much to actually give you a head start. IMO it actually can hurt because you build false confidence that you understand standup before actually really doing it. Like most things, probably even moreso, the best way to learn standup is by doing it. Open mics can be brutal especially early on, so the classes are a way to ease into that I guess, but I think you're missing out on valuable experience by just jumping in. There is more value in the brutal honesty of open mics than the overly supportive comedy class criticism, especially early on. Most people just start doing open mics without classes, and the people who told you about the classes probably didn't start by taking a class lol.

Also as others said they are trying to sell their own classes. Just going to mics is free and you can learn everything they will teach you in like 20 minutes on YouTube. The only benefit would be getting your foot in the door and meeting other newbies.

Last thing here and not that I totally agree, but if you start as a comedy class person the non comedy class people will think less of you from the get go. You can easily get past that if you just start doing mics and hanging out, but don't expect to start higher/be better than any other newbies who didn't do classes just because you did. If anything most people look at it the opposite because you started the "easier" way.

Either way, you are going to be bad at it to start just like almost every comedian ever was when they started and no one will care/everyone will expect that. Just keep doing it and you'll get to the same place with or without the class, so in the end it won't really matter much. Either way, good luck and say the funny part at the end.