The difference is, that isinstance() is also True if the object is a instance of a parent class of the class. 
```python
>>> class Foo(str):
...  pass
... 
>>> f = Foo()
>>> isinstance(f, Foo)
True
>>> isinstance(f, str)
True
>>> type(f) is Foo
True
>>> type(f) is str
False
```
I am not absolutely sure, but I think in this case we only want to test for the class and not for the parents. So I would stick to ```type(...) is ...```