Fallback plan: Spare gateway?

I have U-verse Internet-only (6 Mbps) service via a 2-Wire 3600HGV RG. The other day I was in a thrift store where I saw an ATT 2-Wire 2701HG-B RG. Since it was only $1 I bought it. My idea was that if my RG ever bites the dust I'll have a potential cheap replacement ready to go. In the past, I've done this with DSL service.

My question is, "Was this a waste of a whole dollar?" Would ATT force me to purchase a new/reconditioned RG from them or can one provide his own (used) gateway? Is the 2701HG-B compatible with my level of service? Thanks!