I wouldn't say they are a "MUST", but they are definitely something that you "SHOULD" have. They will save you a lot of money in the long run. If it saves you from one crash, it's paid for itself.
As for the best sim, it all depends on who you talk to. My opinion, AFPD, G3 and Reflex are about the best sims out there. I like Reflex, but that's just the one that I have, I'm sure the other ones are good to. Here is a picture of a heli in Reflex (Raptor 90).