From what I understand (given that I have only 1 device that needs connection) - the USB can be plugged in, connected and left as is throughout the day- and the machine will have a constant on connection, and being that the USB draws power from the PC, no battery issues.
However a mifi - will run out of batteries in about 4-5 hours, and also will go into a sleep mode, whereby if I want return to my computer and want instant net access - I'll have to first turn on the mifi wait a few seconds and then get net access
Perhaps things have changed since I last had a mifi - please let me know
thx