Most likely
Data transfer when roaming is very expensive (as everyone knows)
Due to this, a SIM that downloads a lot can immediatly rack up a cost of several hundred to thousand dollars.
Its for this reason I'm 100% sure that amazon monitors usage and the second one of the SIM cards goes above a certain threshhold without downloading books they'll block it, and send you an e-mail. (or just ban you, depending on how nice they are...)