I am using an ANTUSB-m in the USB 2.0 port of my Android 4.2 device. With ANT USB Service 1.3.0 installed, the USB-m is detected and I am able to send and receive ANT messages through it.
Is your Android device API level 12 or higher (Android 3.0+)? For ANT USB Service to appear for you on the Play Store, your device must have USB Host support.
This thread provides some information on how to check for support.
Also, have you tried plugging out the USB-m and plugging it back in after you install ANT USB Service?