I've heard of it, but know nothing else about it.
Testosterone levels in an individual are usually the result of both heredity and enviromental factors, although I don't know which has a greater effect. Obviously you can't do anything about the DNA your parents gave you, but have you tried other things that might increase your testosterone level?
I don't know what kind of shape you're in, what your diet is, or how much you exercise, but have you considered changes in those areas to increase your t-levels first? Rather than take a drug that might be unnecessary, expensive, and have unwelcome side effects?
I don't have documenation at hand, but I have read articles in health and science magazines about t-levels. If you eat a reasonable diet with moderate intake of fats, maintain a good body weight (I know the "ideal" can vary by person), and get aerobic and anaerobic workouts three or four times a week, and your t-levels are still low (according to a medical professional), then a testosterone supplement might be useful. If you are not up to par in any of those three areas, why don't you see what you can do about your health -- without the drug first -- to see if your libido will improve.
I came to the exercise game sort of late, when I was in my early 30s. I was always thin (but little muscle) so I was lucky that I started exercising and paying attention to my diet right about the time most guys notice things might be starting to slide.
I've continued that and it seems to be paying off. No decline in the libido area. Luckily. I can't remember ever having my testosterone level checked, but I might just ask my GP about that during my annual physical next month.
My personal recommendation is that you do a self-evaluation, and if you are otherwise in very good health, eat right most of the time, and get lots of exercise but still have a low t-level, THEN consider a supplement.
Good luck!