the T4 has really low latency as it’s mainly just passing the data from the device you connect to the T4, to whatever it’s connected to the MIDI output ports. the host device is mainly responsible for sending the data with less latency/jitter as possible
i’m afraid not, as it will only work when connected to a computer (for both power and data transfer over USB). having said that, you could use any other device that has a USB connector and works as a USB host 
if you look for something that does not work over USB, you do have few options, including this one which could be back at some point in the future
