I'm a 23 y/o male asian and I shall help with your paper.
No I did not listen to metal before BM, but I do now. Somehow BM made me love the sounds of hard guitar riffs and drums that were just loud sounds to me before this.
No I did not listen to any idol music before BM. Now I listen to SG a lot (A LOT), though I haven't tried listening to other idol music or it's just doesn't captivate as much. Somehow SG sets a very high standard for idol music in terms of their song quality and also live performances.
At first, OD and 4 no Uta didn't really clicked me at all but ever since I played the full album over and over again in my car/ at my home, I found myself loving the catchiness of this song. Now, everytime I saw the number 4, I would say yon instead of four.
When I first watched Gimme Choko!!, I admitted that I was like "WTF?" then decided to brush it off. The next day, I was browsing through YT and found Megitsune & IDZ, and I CAN'T STOP LISTENING TO THEM THE WHOLE DAY. Then I went back to Gimme Choko!! and surprisingly I find myself headbanging in front of my pc screen. So, I guess I could say that the first thing that attracted me to the band is the uniqueness of the band.
I recommended them to all my real life friends through whatsapp (gotta share all the videos :P ) and every time they decided to hop a free ride in my car, I only have one rule which is "I control the radio and that means BM songs the whole ride". My FB page, insta photos are now filled with BM stuffs as well.
No question/doubt about their authenticity at all. They may not be your 'typical" metal band, but they are a legit metal band. They described themselves as kawaii-metal and they defined it perfectly as well.
Sorry I don't know who Animals as Leaders are so I'll pass on this question. :P
Hope this helps :D