In this particular case, there is no difference: you will see the output of roughly the same level of detail (i.e. it tells you that something that was expected to evaluate to true has evaluated to false). Same goes for
Assert.IsTrue(obj.Foo);
and
Assert.That(obj.Foo, Is.True);
Your team should pick one style of assertions, and stick with it throughout all your tests. If your team prefers the Assert.That style, then you should use Assert.That(obj.Foo, Is.True).