As far as i now, the d4 replaces the mosquito.
when i bought my computers, i had a look at the websites of the producers. usually there are demos, where you can see the display and its functions during a dive. i found this very helpful, because you can see if you understand it easily and like it or not.
have a look at these threads:
http://forums.deeperblue.net/freediv...ws-report.html
and
http://forums.deeperblue.net/freediv...computers.html
maybe you will find some valuable information there.
marc
