The V3 and V7 are completely different beasts so you can't really compare them. The V7 includes accelerometers and the newest Ver 3 firmware uses these for gust filtering. The feedback I have heard from V7 users is that it is an outstanding vario, particularly with the new firmware.
The V3 is a great basic vario. The connections are simple, 4 screws, two wires and a TE tube connection and you are done. As long as your TE system is working properly the vario does it's job.
Dave Springford
www.foxonecorp.com