I did some testing to check performance of the storage.
For the Huawei tablet, I downloaded an app from the Play Store called "SD Card Tester", by samliu720. I ran the following tests on the tablet using several cards I had available:
<For the results below, all speeds are in units of MB/Sec.>
Huawei internal storage: Write: 134, Read 170. Wow, that's very nice.
256 GB "Samsung EVO+" ebay special: Write: 12.1, Read 27. Wow, that's horrible!
32 GB SanDisk Extreme: Write: 70, Read: 61.
As a point of comparison, on the laptop, I downloaded a program called SpeedOut from cam-do.com.
256 GB "Samsung EVO+ "ebay special": Write: 9.5, Read 17 Even more horrible than on the tablet
32 GB SanDisk Extreme: Write: 61, Read: 74.
So the lesson learned is that you get what you paid for!! I paid $29 for the Samsung 256 GB EVO+ card on ebay. It arrived in packaging that looked in every way like it was legitimate Samsung packaging and everything. In reality, it must be a fake.