Why is cyclopropylmethyl radical opening so fast?

Ring opening of the cyclopropylmethyl radical is [reliable and fast](http://pubs.rsc.org/en/content/articlepdf/1993/CS/CS9932200347), and so has been used as a radical trap and a [radical clock](https://en.wikipedia.org/wiki/Radical_clock).


Could someone please explain what exactly makes this reaction so fast, besides the ring strain? Why is the anionic ring opening slower?


[![enter image description here](https://i.stack.imgur.com/fDPLp.png)](https://i.stack.imgur.com/fDPLp.png)


