I'll provide some food for thought, as I take a different view on handcuffs.
When it comes time in the draft to your top RB's handcuff, the other available RBs will all be either other handcuffs or low upside guys who will never be an RB1 or RB2 even if the starter goes down (Woodhead, Sproles, etc.). I don't draft those low upside guys, so I'll consider this a debate between drafting your top RB's handcuff or somebody else's top RB's handcuff. You talked about the handcuff being an insurance policy if your guy goes down, as the backup will then be a RB2 or even RB1 in some cases. You're exactly right. That security feels good, but is it objectively important? I'd argue that it isn't, and I'll explain why.
The decision to draft your player's handcuff vs another player's handcuff comes down to the amount of variance you are willing to accept as an owner. Drafting your own player's handcuff lowers your variance, drafting somebody else's increases your variance. Its a case of high risk, high reward vs low risk, low reward. For argument's sake, lets say if a RB1 gets hurt, the handcuff becomes a RB2 and if he doesn't get hurt the handcuff is worthless. You draft your guy's handcuff. At best, you have a RB1. At worst, you have a RB2. Low risk, low reward. Suppose you pass on your guy's handcuff and draft somebody else's. At worst, you have nothing. Your guy gets hurt and the other guy's handcuff ends up being worthless. But at best, you have a RB1 AND a RB2! High risk, high reward. The question you have to ask yourself is what kind of variance you prefer.
I'm a statistics driven guy, so my answer to that question is that I don't care. Variance means nothing to me, I only care about expected outcome. Suppose i have $100 and you offer me a betting choice. Bet #1 has a 10% chance of paying me $1100, and a 90% chance of me losing everything. Bet #2 has a 50% chance of me winning $100 and a 50% chance of me losing $100. I'm taking bet #1 every time. The expected outcome of bet #1 is $110, the expected outcome of bet #2 is only $100. I have a higher risk of losing it all on bet #1, but the reward is higher, and subsequently the variance is higher. I will never end up with $100 or $110, but these expected outcomes help us value the quality of these bets. In a perfect world with unlimited capital at his disposal, a good gambler cares nothing of variance and evaluates every bet on expected outcome.
So let me relate this back to fantasy. I rank my running backs based on their value. Knile Davis, Jerrick McKinnon, and Deangelo Williams are very close in many popular rankings and are actually right next to each other in my rankings, in the order I presented them. There's a reason I rank them this way, even though they are very close. In a vacuum, I'd rather have Davis over McKinnon and McKinnon over Williams. I believe the expected outcome of my season will be better if I have Davis over the other guys. So when I'm on the clock in the 12th and drafted Bell in the first and these three guys are the three best players still available, who do I choose? Davis, every time. Drafting Williams would certainly lower my variance, but it would decrease my expected outcome.
I develop my rankings based on a combination of subjective and objective variables. Those rankings change often, but when I sit down to draft I have to trust those rankings and draft in a way that maximizes my expected outcome. Now, that doesn't mean I draft like a machine and purely take best player available according to my rankings. Being forced to start a certain number of players at each position and having only starter's points count means there are times when reaching is necessary. If I take 4 running backs in the first 4 rounds and come round 5 I see that another RB is my best player still available, I'm jumping him with the next best player at another position, as filling out a starting roster is important. But for our discussion here, we are talking bench players. In that case, I'm purely looking to maximize expected outcome.