I have at least a dozen in various sizes and shapes, so far I've only managed to crack one of them up at the very top of the rim. I still drink water out of it, yes I am an idiot since I refuse to throw it away. I figure why toss it when I still have a chance to drink out of it but no worries since I only serve myself in it.
I'm surprised I haven't had any issues with them, we're not the most careful people in our household and living in earthquake capital of the world doesn't help either. We drink (alcohol) shots, wine and whatever else comes to mind out them.
I just had a hot cup of coffee (202 degrees) in the cracked one, followed by an ice cold water in the same glass without issue again for the 6th month in a row. I do pre-heat the cup and pre-cool (slowly) before each use but I do that anyway with all cups and glasses.
I do think some are thinner than others and slightly different in size and shape since they are "mouth-blown".
Never understood that "hand-blown" term myself since glass is really not blown by peoples hands
