I have that SPL meter and it works very well, I haven't checked it against the Radio Shack SPL meter I have, as the Radio Shack meter has compensation files available for it for better accuracy. I know this might be confusing you so don't worry about the differences, the Extech works and that is all that matters right now.
If you do want the Radio Shack meter for these compensated numbers, I linked to one awhile ago that is available from sonicboomaudio.com for those of us in Canada as the radioshack meter isn't available anywhere else up here.
