I used the Velocitek device for training in Singapore before the A-Cat worlds. Since I was always out by myself needed to be able to guage what my speeds were and what were appropriate targets. Built myself a fair picture of what to expect.

For example, when I really should be on the wire and when not. But also when to go wild and when to stay flat.

Used the unit at the worlds and based on my training and utilisation of the my own developed "polars", was on the pace.

Thoroughly recommend the Velocitek. You will find it very useful for downwind with the kite. Eg, when to have the crew on the lowside, on the highside, and when on the wire. In my experience I see a lot of boats try and heat it up with the crew weight not in the right place. Eg having crew on the low side and skipper sitting in middle of tramp will get the hull out of the air early and you will be able to go downwind at the same speed as the other boats but at a deeper angle, thus achieving better VMG in lighter marginal conditions. Did this many times in Singapore and would smoke everyone.