The nicrew actually has good reviews for freshwater. It is cheap but effective and I have talked to many people who have used it and was recommended it for my planted tank. It just doesn’t have all the bells and whistles that the more expensive lights have.
But by that logic, getting a cheaper light for a marine tank, even if it seems as effective, is not the best idea.
Yes you still want a good test kit. You need to have a good idea of parameters for any corals or even fish. Lps and nps especially, both of which are very susceptible to swings in parameters. And even softies and macro will dies quickly if something is off.
If you can’t test for a problem, you have no idea what to fix.