Yes, the difference is most significant for small arrays.
```
In [8]: a
Out[8]: 
array([  1.,   2.,   3.,   4.,   5.,   6.,   7.,   8.,   9.,  10.,  11.,
        12.,  13.,  14.,  15.,  16.,  17.,  18.,  19.,  20.])

In [9]: %timeit np.add.reduce(a)
100000 loops, best of 3: 2.46 us per loop

In [10]: %timeit a.sum()
100000 loops, best of 3: 4 us per loop
```
That's enough for me.