Question 1

With only one connecting point to the guitar, it seems like the guitar needs to be held in position with both hands. How stable is the guitar?

Accepted Answer

The point of connection is movable, so the balance is not really unstable.  But I do keep my hands on the guitar.  I can say that it has really helped my back.

Question 2

How long are the bendable supports?

Accepted Answer

About 20 inches long, plus another 1 1/2 inches for the little buckles. Of course, the supports can be made to "mold" around your own personal body contours. 
BTW, in my opinion, this is an EXCELLENT product. I can play my alto or tenor for hours without even the slightest fatigue on my shoulders. Of course, there is NO strain on the neck. The only slight drawback is that it is a bit more, shall we say, conspicuous than others, so some might consider it appropriate mainly for practice sessions. But, the comfort makes it all worth while, at least for me. I hope this helps.

Question 3

Can you spin the guitar like on the zztop video?

Accepted Answer

No

Question 4

Does this have different  sizes ,or is it one size fits all... im a big guy

Accepted Answer

It's one size fits all, but it is fully adjustable and all the straps are all quite generous in size, especially the one that goes around the chest. In fact, the manufacturer gives instructions on how to "burn" off any unnecessary lengths so they come out neat and not frayed.  
This is, without a doubt, THE most comfortable sax strap I have ever owned- and I've tried plenty of others. I used to have issues with my neck but not anymore! It is also extremely versatile and allows great freedom of movement for yourself and the instrument.  I use it for both tenor and alto and strongly recommend it.

NEOTECH Sax Harness

描述

常见问题