SpaceX has more experience than anyone else in lighting dozens of rocket engines at once. They've never had a Falcon Heavy failure in 5 years of operation.

It's not the number of engines that's the concern, it's the sheer power. This is the most powerful rocket ever made. It produces as much thrust as two Saturn Vs. The danger here is that something on the ground gets damaged by the sheer magnitude of this thing. And failure here is very possible.