The CS741U is an Ethernet interface upgrade, which operates at 100 Mbit/sec, or about 6 Mbyte/sec sustained throughput. In normal use, there is no discernible difference in performance between the CS740 and CS741. However the Ethernet is transformer isolated to 1500 V peak, and so there is no galvanic connection to the PC. In addition because it is Ethernet, you can operate the Cleverscope on a network anywhere (even on the other side of the earth!).
The CS741 replaces the CS740 USB module. It supports 10/100 Mbit/sec auto switch, automatic TX/RX selection (MDI), no cross over cable required.