Or derivative platforms... I'm sure everyone here heard of BitMEX, but still, I wonder — is it really as good as some people claim?
It depends. For someone, this exchange may be good enough, while others may say the website is awful. So, in case you're wondering about this particular exchange, try to find some websites or sources which will provide you with bare facts or arguments. The likes of Bitority feature expert opinions and recommendations. And they have reviews on many popular exchanges, including BitMEX
https://bitority.com/review-of-bitmex/ . There you're likely to find the answers to your questions. It says that the exchange is secure and reliable, and has fast-responsive customer support. Also, it allows for margin trading, but it might be challenging for newbies. It doesn't provide services to the US users though. So, that was a brief overview, check the details on your own.