Real good posts so far. Thanks. I wanted to mention that I emailed Mars with the question of "lets say the m2's battery doesn't last the 15.5 years that it should? Will it be replaced free?"
The response was short, and in slight broken English, but essentially the response was that they would replace the battery free of charge if it was found after inspection that was the reason the unit would not power on any longer.
Honestly tho, in any of these devices, in 10 plus years if you need a battery change, its possible the batteries in these devices are no longer manufactured, unless its a real common battery they are using in them. No clue what type of battery is in any of them.
Again, what sold me on the Cypress wasn't only the track record, but the fact their website hypes their product up with multiple high quality photos of the manufacturing process and how their "attention to detail" is impeccable etc. They really try their best to show and tell the quality of the manufacturing / quality control.