I use one, and I think its a benefit. On my boat i set the diamonds to a guess of what the conditions might be. I think that it makes a big difference on my boat.

I also question the accuracy of the loose gauge, however i think what is most important is that it reads the same every time. I think that you should look at the tuning guide for a guideline but come up with your own numbers overtime. With that in mind I think it's important to use one gauge on your boat and not use multiple ones. Find out what works for you and take notes, The gauge will help you repeat the same settings when you want to.

I use the Harken rigtune. several friends have put their loos gauges on my boat to compare and seen similar tension numbers. However one guy put his device on my boat and it read several hundred pounds differently, if I had used his gauge one time for my settings, it would have been far different from what I was expecting.