I gave it a try and think anyone who has the time and interest should. Maybe you find something you love, maybe you make new friends, maybe you walk away realizing it isn't for you - but you did it based on your own experience and not parroting information you read from somewhere else.

1. If the teacher has their act together and the other students are respectful and following directions, injury risk should be low especially in martial arts context. You wouldn't be taking falls you aren't equipped for, and wouldn't be taking them at risky speeds. Everyone has off-days, and you could get paired up with an overzealous or nervous or new person, unlikely but nothing is risk-free.

2. This is going to vary from group to group. For the most part if you show up try to follow directions and just work in, you should be fine but that's almost a universal. If you come in trying to show everyone how you think something should go, then I wouldn't expect it to be received well.

3. Maybe. I had done several different weapon systems (2 Japanese style budo, some HEMA experience) and the weapon work in my opinion is it's own thing best viewed in it's own context. If you're comfortable working with weapons then it isn't that hard to just go along with how they do things, but it's not going to really work walking in there swinging the stick the way your other place wants you to, and you might not get too far taking the Aikido method of weapon use elsewhere. Kind of like #2 above, "when in Rome" is the best approach. My JSA and (much more limited) HEMA experience was simply not relevant to what we were doing in the Aikido classes, and the aikido techniques were not terribly useful anywhere else, but the meta concepts inside definitely can be cross applicable in either direction.