Is the Verizon Edge program worth it for me?

[iMore Question]

My wife and I have iPhone 5S. We aren't typically the type to upgrade to new phones each time Apple releases one. Our previous phones were the iPhone 4, so typically we upgrade every other generation. The Verizon Edge program is intriguing to me because of the $25 discount offered on the 10GB shared plan. Currently I'm on an old 6GB plan which is the same as the 10GB plan. If I end up signing up for Edge, it seems that with the discount, it would only be costing us around $2 per phone assuming we get the 16GB models. What is the drawback to this Edge program if we plan to keep the phones for 2 years? Thanks!