TCP mode load balancing would treat each TCP quad (source ip/source port, dest ip/dest port), stream, or flow as a "session" or in other words, the TCP stream is the basic unit of TCP load balancing.
You can enable the stats http interface and monitor that in your browser for some useful metrics such as session count etc. There are also tools such as hatop that will monitor the stats socket (unix domain socket) and print a summary on the console. See "stats *" directives in manual... http://haproxy.1wt.eu/download/1.5/doc/configuration.txt
