I have low SHBG - it was 12 in my last bloodwork - and that is pretty much where it's been for the previous ten years, but I have no trace of metabolic syndrome, and I am not diabetic or pre-diabetic.
With low SHBG, I do not "feel" my TRT at all. On TRT and with good blood numbers for free T, total T, and E2, I still have low libido, and can't build any muscle or lose any fat. It is like being "low T" even while on TRT. Oh, and guys that think low SHBG is "better" and builds more muscle need to walk a mile in the shoes of someone with low SHBG. We would not wish it on our worst enemies.
The only reason I am still on TRT is that I know it's healthier long-term to have normal T vs. low T.
I, too, have low SHBG tested through years of labs (usually 10-15). No metabolic syndrome, no diabetes, etc. Very good health overall, lean, low body fat, low inflammation, etc.
In experimenting over the years, I found that I subjectively felt better with frequent injections - more stable I suppose.
Here's what I know about being on TRT. Before I started, despite several years of working out (much of that time with a trainer), using protein powder/shakes, etc., I had an inability to gain muscle and relatively low endurance. My body fat with Dexa was ~24%.
After being on TRT for a few years, much better endurance and much better ability to gain muscle, lower resting heart rate, etc. While staying at the same weight the whole time (~190-195), my body fat dropped to about 12% (Dexa). Which means I converted about 23 lbs of fat to muscle. That -objectively- didn't happen without TRT.
Further, due to recent surgery for prostate cancer, I stopped TRT entirely for about 6-7 weeks. About three weeks into that period, I could absolutely feel a sharp drop in energy, felt much more tired, etc.
Does TRT make me feel super fantastic 24/7 and solve the world's problems? No. But it has definitely, objectively, improved my overall health.