Yes that model is a desktop model HDD. Although I've never had good luck with Seagate. I've always opted to go for Western Digital Black drives. Additionally, their green/blue series aren't bad but your sacrificing performance to gain strengths in other areas i.e. energy savings, more quiet, runs less hot, etc.
I agree, go for the larger drive. If you can get a few then RAID them. I have a stack of WD 1tb drives that I took out of new DVRs. They work well in RAID and have stable lifelines.