I'm an investor in Swingbyte and have been using it for the past 6 weeks or so. I can answer a few of the questions on here -- though please understand that I am not one of the developers and these are only my impressions. Happy to answer any more you may have as well.
I have been golfing since I was 9 years old (now 44) and have tried my share of teaching aids, swing trainers, and have been utilizing Trackman, Flightscope and similar for a few years. I'm a 4.8 index. When the developers came to me, introduced through a mutual friend who is a PGA teaching pro, I was skeptical. I've seen a number of electronic gizmos that do very little. In fact I put off the meeting for about a month and only did so as a favor to my friend.
Alex, Brian and Nathan dropped one of those golf matts with a ball on a string right in my living room, attached the Swingbyte to my 3-wood, and I hit a few. After each swing, within about 2 seconds, the tablet 'chirped' letting me know it captured the swing. They then walked me through the features...
Swingbyte is very different than Trackman and similar launch analyzers in that it models the entire swing in 3-D. This is something I had not seen before anywhere with my own swing. I've utilized video (at Golftec) and have seen my swing... but with this I can see precisely where I am at every point along the swing plane because the Swingbyte is on the club itself. So down the line, face on, and even a view from above is instant and accurate and can be rotated in 3d along any axis -- it does not rely on the positioning of a video camera. The visual analysis can be stepped through point by point.
More interestingly, I can see the swing speed at every point along the swing plane... and could therefore easily visualize and see the data of my swing acceleration. Like most amateurs my maximum swing speed was just before the ball -- casting slightly -- instead of accelerating through the ball. This is something that I have used the Swingbyte to address... and while I have read about a million ways to create lag I never had a way of measuring the difference in swings except by watching the ball flight.
Also really interesting is a Tempo feature that measures very precisely the total time of the takeaway to top of swing / top to impact / and overall swing time then gives you those numbers plus the ratio of backswing to downswing. Again, because the accelerometers are on the club tempo can be measured precisely. We've begun gathering Tour data on Tempo with some surprising results (see that Ernie Els article about his speed vs tempo and you'll know what I mean). So this is the other piece of the puzzle that I've found very, very useful in practicing.
As for the speed measurements....
Swingbyte sits just below the club grip and weighs less than an ounce. Once it is on there I don't notice it or feel anything different in the club and I've put it on a bunch of my friends' clubs and no one has swung differently. The shaft of the club moves at a rate slower than the head, but by putting in the club data (length, type, shaft) the club head speed can be interpolated very accurately. I've been on a set up of Trackman / Flightscope / Swingbyte at the same time and have found that Swingbyte was consistently +/- a few MPH. But here is the key point -- the swingbyte is *internally consistant* -- meaning that from swing to swing it reports back the same baseline data. So improvement in swing speed can be accurately tracked even if the absolute swing speed is off a few MPH. Whether I'm swinging at 98 mph or 94 mph doesn't much matter to me... but improving upwards does.
Swingbyte is not a launch monitor nor is it intended to be such. For golf simulation and and club fitting it is not nearly as useful as Trackman or Flightscope. You're not going to get ball speed or spin. Swingbyte is meant to be an instructional and *swing* analysis tool. And in that regard it is far superior to Trackman as it monitors and reports the entirety of the swing, not just launch conditions. It is the best learning tool I have ever seen -- totally mobile, usable on the course itself (my swing is of course different on the tee box than the range), and simple to use. And that is why I surprised myself by investing in and helping -- to the extent I am able -- the company get off the ground, so to speak.
I'm hugely excited that they have started shipping the Android version and the iOS should have App store approval very soon. Happy to answer any further questions.