Purchased one of these to communicate with a serial device, and discovered it wasn't working. Deeper analysis showed that both connectors appeared to be incorrectly wired (pins 7 & 8 bridged on the DB9F connector, pin 20 on the DB25M connector not wired). Monoprice support was great with an RMA and provided another cable. Unfortunately the replacement cable had the same issue. This may work if you only need TX/RX/GND, but if you need RS232 with handshaking this will likely not work.
The following is how (based on pinouts from several websites) a DB9 - DB25 Null Modem Cable should be wired:
DB9 Pin 2 - DB25 Pin 2
DB9 Pin 3 - DB25 Pin 3
DB9 Pin 4 - DB25 Pin 6
DB9 Pin 5 - DB25 Pin 7
DB9 Pin 6 - DB25 Pin 20
DB9 Pin 7 - DB25 Pin 5
DB9 Pin 8 - DB25 Pin 4
I'm still a happy Monoprice customer and will continue to buy their products. To the Monoprice technical staff: it might be worth investigating this further. I don't know every RS232 cable configuration, but having pins 7&8 on the DB9 side bridged seems very strange.
PROS: High-quality molded plugs and cable
CONS: Incorrectly wired for DB9 to DB25 Null Modem