hey
well , as for a beginner , I think you can use one only no worries , but , for a power measuring , go for 2 of them ( and also for more confidence , you'll be able to compare both against each other to see if there is any drift )
as Dave said on the 50$ shootout , buy either of thous :
1) Extech EX330 (the winner)
2) Amprobe AM220 ( the 2n'd winner )
oh , and BTW , I would recommend you watch all Dave's episodes , you'll learn allot .