Most of the cartridges that they sell are reproductions.
If you're happy about getting a non-original game then OK. But if you want to go down that road, you could get a Sunmark multicart, or just SIO2PC hard/software.
Pengo is not so rare (5/10) and they do appear on eBay fairly often.
Buying reproductions, like Telegames' ones, is not my cup of tea.
I played Pengo a long time ago, and, as a true collector filled with nostalgia, it would be an offense to buy such a copy
I see B & C has it for $9.95 (new in box) and Bravo Sierra Computers for even less ($7.50), though they don't tell about condition or if it's boxed... Ben Smith of Bravo Sierra Computers is a great guy, maybe you should drop him an e-mail and ask him.