Lately I've been in a slump - Low energy, poor mood.  Other symptoms which I would prefer not to go into but lead me to believe that I'm running low on testosterone.  I'd prefer not to go to the doctor for this, not without trying other stuff first.  A quick google search turned up this product from GNC which is supposed to boost T.

Is it effective?  And if so, will using it setting myself up for dependence to maintain a proper hormonal balance?

Don't waste your money. If you could increase test levels with an OTC pill, hormone replacement therapy wouldn't be the industry it is.

If you decide to do a test booster cycle, try something NOT from gnc, do more homework, the n if you decide to do a cycle of it, you also need a pct, or estrogen blocker other wise you will grow moobs, and you'll estrogen level will sky rocket while you won't produce as much testosterone, it's a never ending cycle

Natural help would be doing back squats in the gym, it boosts test by 33% naturally

90% of supplements are bullshit. "Test boosters" made of plant shit, like this one, are in that group.

Testosterone is a pretty important hormone so you can be sure if anything OTC actually affected it, the FDA would regulate it into being prescription-only real quick.  People would already be abusing it.

Another vote for doing squats and/or deadlifts; also watch out for alcohol consumption, smoking, other areas of health too, such as sleep quality/quantity.  Lifestyle can affect T levels to some degree, but if it's a real medical issue a doctor is the way to go.