Pretty much all SD card makers will void the warranty for cards used as boot drives in an SBC (with the possible exception of high endurance cards, but even that's uncertain). That's simply not their intended use.
The whole A1 A2 thing is another story. I purchased an A2 card, knowing that my current hardware would not fully support it, but I assumed it would still be at least a little faster than an A1 card. It wasn't.
In every test but sequential write the SanDisk Ultra A1 cards were faster than the SanDisk Extreme A2 card, and since we're comparing an Ultra to an Extreme, the faster write is no surprise. What was a surprise was in sequential read, and random read and write IOPS, the much less expensive A1 cards were faster. Granted, it wasn't a huge difference, but you're getting less performance for more money.
The IOPS was particularly interesting, because I would have thought that would be more about the internal controller than anything external, but that doesn't seem to be the case.
When I contacted SanDisk about this they were very cagey. They would not openly admit that the A2 card could only perform well in specific hardware, but they kept pushing me to buy a particular model of their card reader (which is one of the very few A2 certified products available now). So I ended up returning it and posting a review on Amazon about the A2 card's dirty little secret.
So yea, don't buy A2 cards unless you have a very specific device that is A2 certified. If you already own one and it's too late to return it, don't fret too much because they are still much faster than standard Class-10 cards, and close enough in performance to A1 cards that the difference is probably not human perceptible (perceivable?). You spent a bit more than you needed, but it's still a fast card.
My mind is like a browser. 27 tabs are open, 9 aren't responding,
lots of pop-ups...and where is that annoying music coming from?