I think baby signing classes are one of those things that you can't tell how it will work out for you IYSWIM. Loads of people I know did it, it was quite the done thing around here for a while, some loved it some hated it.
One family I know did it with both kids, the first DS took to it really well, somehow didn't have any of the 18mths+ tantrums etc and she swore blind it was because he could communicate so no frustration but that theory went out of the window when their second, their DD who also did baby signing had worse tantrums that I have ever seen before. (I admit that I did have a small chuckle to myself about the many self righteous 'our DS doesn't need to tantrum because he can sign' type conversations I had with her!)
Another family I know did it with their DD and again she took to it really well (started at 6mths and went weekly til about 16 months), could sign all sorts really early on and it made life easier to know when she was hungry because she could tell them, but now at nearly 3 and and half she still relies on her signing and having started preschool none of the nursery nurses know what she is trying to say. Her speech is actually pretty good when she does speak but she chooses to sign, so that is now an issue for them.
Then there were quite a few friends who just did one or two terms of it as a nice social thing to do with baby, a singsong, some fun signs and then coffee with some other mums afterwards and tbh those are the people who seem to have enjoyed it most
I think it just depends what you want to get out of it, if you want a fun activity that might help a little with communication but mostly have fun together then I'd go for it.
If you are hoping to use it to improve any future behavioural issues etc etc you may be disappointed (but would have still had a nice time at the classes).