Chris is a USPTR Coach and Professional Stringer with over 10 years of experience. Below is his review on the Tennis "String Thing" tool that is being sold on TV.
It is designed to be rolled along the string bed and is claimed to be made of a very durable plastic material. I was a bit skeptical when I saw this $20 product...
Tennis String Thing Review
I purchased the "String Thing", hoping to find a product that could make the stringing process faster.
After stringing a racquet, I spend a few minutes straightening the strings. While the strings are relatively straight coming off my machine - they are not perfectly aligned. The straightening is more for aesthetic purposes than for performance. I do not subscribe to the belief that a few misaligned stings dramatically affect shots.
Dealing with Crooked Strings
The most prevalent issue after stringing is the bowing effect on the crosses (horizontal strings). Straightening is usually done the fingers or a flat tipped awl. After using the String Thing device on a few string jobs, I found it to be less effective than using an awl or your fingers.
This device does a reasonably good job on the mains (vertical strings)...It makes little to no difference on the crosses.
Results
The effectiveness of this device also depends on the type of string used and its tension. I tested this device on multifilament, nylon and polyester strings. This device is pretty much useless on polyester strings and marginally effective with multifilament and nylon strings.
The device works better when the tension is lower. I found that for this device works best when you need to use strings strung in the low 50s or lower range.
Conclusion
As far as using this device on the court, I believe that using your fingers is a better option.
If the string bed is completely misaligned after every point, you need to have your racquet restrung. For players who hit with pace, a very loose string bed typically indicates imminent string breakage.
Editor's Note in 2019
If you have sensitive fingers or need to straighten lots of strings per day, this "String Thing" pocket tool might be worth a try. The average poly string tensions have dropped since 2011 when this article was written. Similar to the purpose of the old school Pete Sampras "string savers" to extend the life of your string. If you find that several of your poly strings are misaligned, often that is a sign that it may be time to get a new set of strings.
Counter-Point from Stringer who loves it:
YouTube Review by Inspired Tennis