I was reached out by a contractor and went through an on-site interview in one of the locations in PA. Similar as to what you may have read from others, it first was a group interview (activity-like) and if they see you are fit, you'll continue on to the next part which is like a speed-dating but more of an interview. There are some who said it was hard, though in my perspective, it was more because of nerves and it was fast so I didn't think it was that hard to begin with. My advice to you is that be confident, passionate, respectful and kind to the interviewers and those who are going through the same process as you and ask lots of questions! They definitely notice the little to big things :)

It was a good experience. Very different than other companies. It was a group interview. You get to know other interviewee before the group interview starts. first we had group interview, it was consists of a group project that was to make a structure from a lego set, and later 5 minutes long interview was done in speed dating setting.