If the pilots fly them, now, then you can know they are safe. Collectively, and in the US there are unions, they have 10,000 times more knowledge and information on this than we ever will.
That said it was never a particularly good performing plane that among other things has very high take off and landing speeds and an obscure flaw where the ailerons may lock up. It's likely the MCAS caused this condition. Again if pilots return to the plane then you can be sure they are safe. Maybe they won't. I was just a grunt but I worked on mechanical systems my whole life and with controls engineers for 20 years.
It has been flying for 50 years with a great safety record. It isn't inherently unstable. This latest iteration of the plane is a Frakenplane. It's birth coinciding with a period of now unbelievable safety. There has not been a crash of a passenger plane in the US of a large airliner in going on 18 years when there used to be multiple crashes a year from the mid 60's on.
The response of Boeing and regulators after the first crash, then the second is beyond the pale. Then last week the pathetic little boot licker acting FAA secretary who refused to ground the thing after the second crash and only did when fking Trump said it should be, had the nerve to blame 'foreign pilots' for the crashes. Disgust with the whole affair is justified but know it won't mean a thing. Nobody higher up will pay except Boeing top execs might get a smaller bonus this year. While the whole saga is a good analog for what is going on with the entire system don't get carried away by the story. It isn't like the banking and financial system where crashes have been endemic for 30 years. Just the opposite in fact.
(Smith mentions two 737 crashes here but those were not caused by anything to do with the air frame or its deficiencies but a bad hydraulic servo valve)
The Air France flight 447, an Airbus A330, plunged into the Atlantic in 2009 on a combination of failed sensors and ultra modern flight controls.