the watch is just plain NOT functional for a tri
I think you have some very legitimate concerns as far as using the S625x during a race. But I would hazard a guess that it was conceived and designed as a training tool.
As far as altitude unreliability, I would have to disagree. I think the altimeter is very accurate and reliable. I does require frequent calibration (all do), and is affected by the rapidly changing ambient temperatures, or body temp. If you were to put the watch on your bike and set it outside to acclimate for 15 minutes, then Calibrate it to the current altitude, I would suspect that you would get very accurate and reliable readings, unless a major weather system was moving in during your ride. Many aircraft use barometric altimeters, and airports broadcast a calibration number for them to use, they are very accurate when used correctly.