Let me start by saying I've been using the Digi-Chip 128GB MicroSD in my Fire HD 10 for about three months now, and it's been mostly smooth sailing. The installation was literally plug-and-play - popped it into my tablet while watching Netflix, and bam! Instant extra storage without any formatting needed.
The speed is decent for everyday use. I've loaded about 80GB worth of ebooks, apps, and some HD movies, and everything loads quickly enough that I don't notice any lag. The Class 10 rating holds up when transferring files from my computer too - a 2GB movie takes about a minute to copy over.
However... (and this is a big however) I did have one scary moment where the card suddenly showed as 'corrupt' after two months of use. A quick restart fixed it, but seeing those other reviews about corrupt cards makes me nervous. I've started backing up important files just in case.
The included SD adapter is a nice touch - I've used it to transfer photos from my DSLR camera when traveling. It's these little conveniences that make the product stand out.
Would I recommend it? With caution. It works great when it works, but the potential corruption issues are concerning. Maybe keep your receipts and consider the warranty if you're storing anything irreplaceable.