I have been using the "String Thing " for about six months and I have to say it makes straightening the strings a 10 sec job plus I don't end up with sore fingers!
Visit the website below to see the product and video.
If you are a Stringer then you will need two String Things one for Dense string pattern 20 x 18 and one for Open string pattern 16 x 19.
I use them all the time and I think they are worth it. Saved my fingers! The cost is about £15 each.
You can but them from: http://www.tenniswarehouse-europe.com/