Well Hist Ext requires way more critical thought than Ancient or Modern and you have to really explore and develop your own philosophical opinions on things like D94 has mentioned but if you love history then I think you'll enjoy it because it really is quite an interesting course. So benefit: enhancing your critical thought skills would be useful for literally anything as it makes you more perceptive + good skill for university studies.
Also don't worry about the major. If you choose a topic you like and would be willing to do ~9 months worth of research on, then it'll honestly be fine and maybe even fun (I did mine on American Revolution which I love and I really enjoyed writing the major). Make sure your question isn't too difficult that you struggle to come up with a coherent response but also don't make it too simple that you can't reach the word limit. Just actually get started ASAP and don't leave it last minute to avoid stress but also to get your teacher to mark it. Benefit: my teacher said that this type of research is "the closest thing to university research that you will conduct in high school" so again, good prep but also the flexibility is great because it can literally be about anything you want.
Hist Ext is a great subject and if you put the work in then you will really enjoy it + benefit from it a lot
