The Radio Shack 800 MHz duckie will give you the same or better performance than an actual "brick phone" or bag phone cellular antenna. I've done my own testing in the past with such things - I grabbed some original "brick phones" at a thrift store for a few bucks each years ago, and a few bag phone 90 degree bend ones like the one in the pic above. With a TNC to BNC adapter (and yes I know there is some technical signal loss but it's so miniscule at the scanner itself it's not even relevant - we're not talking about 50 feet of coax from antenna to the scanner), I tested using a Uniden 246T, a Uniden BC200XLT (oldie but goodie), a Realistic Pro-34, Pro-25, Pro-37, and a Pro-43.
Using the 800 MHz duckie resulted in cleaner signals with better noise quieting than using the so-called cellular tuned antennas on almost all the "stuff" I was monitoring. I don't know precisely who makes this duckie for Radio Shack (maybe someone out there does, I'd love to find out myself), but it truly is an amazing thing for the price.
It seems like an actual "cellular" antenna from the good old days of analog cellular activity would make a difference, but for me, the 800 MHz duckie is the best $20 I've ever spent for an antenna for a specific band - and as a bonus it pulls in UHF Lo (~450 MHz) with outstanding clarity and even VHF Hi (~150 MHz) damned fine too.