One of the boats I race on uses the Velocitek. The same boat also has a Tacktick Racemaster like this Tacktick Micronet Race Master: Mauri Pro Sailing
on it as well, both are mounted on the mast.
We use the Velocitek mainly for a quick way to see how changes in sail trim affect boat speed. With the single screen only the helsman can actually see it if the rest of us are hiked out on the rail.
I think the Racemaster is a more valuable tool, in that it can determine the favored side of the start line, has a large number display and beeps when used as a countdown timer, tacking angles, and instantly show wind shifts which can be another tool in calling tacks and jibes. The angled split screen is great so that the entire crew can be on the rail and still see it clearly. What is appealing about either device is that one does not need to have an electrical system to operate them which is nice for small boat racing. The Racemaster has been flawless.
The Velocitek worked for about three outings and then on an especially rough day with every damn wave breaking over the bow and soaking everything on the boat, it leaked, causing the display to fog up. During the race the next day it stopped working at all. The unit was sent back and eventually a new "upgraded" version was returned in it's place. The customer service was slow but they didn't put up a fuss. Being a pessimist I have a feeling, not based in fact, that this was not the first time a "wet dead" unit was returned under warranty. They said that they were sold out and that the replacement they sent us was an upgraded factory rebuild. The electronics appear kind of rudimentary to me. As if some electronics wizard threw the parts together in his basment and then, as an afterthought, tried to find a way to use it in the marine environment. The case appears to be just a modified tiny Pelican style case. My biggest pet peeve with this design is that the case has to be opened everytime you want to turn it on or off. When opening the case all the electronics are exposed to the environment, you literally are operating a microswitch on the circuit board as an "on/off" switch. There has got to be a better solution...
Both tools are great for diagnostics, for example, if we don't feel like we are pointing well, when setting up the Tacktick one can manually input your tacking angle like 90 degrees or 45 off the wind. In an instant it is clearly visible to all on board after a tack if we are haveing a trim problem or maybe we are pinching etc... Maybe the boat feels slow, a glance at the Velocitek can confirm if we really are slow or if the sea state just makes it feel that way.
What kind of boat would you be putting it on? Does your boat have an existing 12v system? What kind of racing are you doing?
If I could use only one, it would be the Racemaster.
Electronics like these can't be a substitute for actual sailing skill and racing tactics. One should look at items like this as just another tool, like a Windex or telltales to assist in sailing better. Do they help...yes. but I have no idea how to measure it.