Has anyone ever used the Mega Bus? [closed]

Assuming you're only interested in the US version of Megabus, given the route mentioned, then their homepage lists that they've transported over 40 million passengers so far! Given that, the answer to your main question is:

Yes

Large numbers of people have used Megabus!

In terms of your edit asking if it's dangerous, the answer is "not really". You can find out all about Megabus's safety and training on their website, which should help reassure you that they're a reliable and reputable coach operator. Given that, depending on what sort of car you'd otherwise drive in, it's potentially safer than driving yourself!