The number of elements required is much less.

The 'standard' summing circuit [0] typically requires an op-amp, which is in itself a multi-element component, and a few resistors. With a memristor, you can theoretically skip the op-amp and just use the passive elements, though an op-amp is likely still needed to read out the very small signals [1].

[0] there are MANY ways to skin this cat, but here is a simple one: https://www.electronics-tutorials.ws/wp-content/uploads/2013...

[1] https://image.slidesharecdn.com/1205-141021211518-conversion...

The opamp is mainly needed of impedence matching. There are several ways to contruct such circuits using just inverters.