Your SHBG doesn't determine whether you would benefit from testosterone or not.
This is a clinical indication.
A low SHBG can occur in the setting of high testosterone, but is not diagnostic of this as there are other potential causes and testosterone can be measured directly so it doesn't need to be inferred from SHBG.
If the SHBG is high, this can mean any testosterone you have is getting bound up by this protein so there is less biologically active testosterone available.
However this is more of a theoretical concern than a clinical issue, and giving testosterone can also lower the SHBG.
In any case neither of these situations apply to you, and it is certainly worth a therapeutic trial of testosterone, whether for libido or other symptoms suggestive of hypoandrogenism.
It either helps or it doesn't, and you can then decide whether or not you want to continue it, but if you never try, it might have really helped and you won't know.