K&M 164/16 Harmonica Holder

I ordered this in order to replace a slightly flimsy harmonica brace that I have been using. I've bought a heavier harp (Super Chromatica) and needed something sturdier to support it - I bought this thinking it looked just the part. The instrument fits very snug within the brace and it is very comfortable to wear but as soon as I start using it live it just flops downwards. The two knobs either side of the brace just loosen more with every breathe. I've tried everything to get them to stay tight but as I only use the harp for occasional songs it gets very frustrating having to tighten and untighten it between numbers. Very disappointed on the whole. I thought it might be because of the harmonica's weight but even when I use my diatonic harps I get the same problem. I've gone back to using the flimsy holder! Would only recommend this for bedroom harp players - not suitable for live performance.