Update:I increased my rating from 2 stars to 3. Upon suggestion of Samsung, I returned the original SD card that I received for a replacement. Before I got a replacement, the first card failed and reported as corrupted. The newer card does have much faster read speed (55MB/s vs 14MB/s originally), but the write speed is still around 20MB/s.If you purchase this, or any other SD card, check performance with CrystalDiskMark or FlashBench on PC with a usb 3.0 card reader, or A1 SD bench or SD Card Test on android. If you're concerned about it being a counterfeit, run h2testw on PC.I would think my first card is just a failure in quality control, but it's possible I had a counterfeit card. I ran Diskinfo Pro on the cards and both reported similar data except for manufacture date which the first card reported as 00/2002 and the second reported 04/2017. It's possible that the card was already partially corrupted at that point, or that it was counterfeit and the counterfeiters forgot to put a reasonable date in that field. The cards looked pretty much identical but the box of the newer card had darker printing and different shaped raised area on cardboard sleeve (see attached image). Those could just be regular variances in manufacturing, but I thought I should mention them at the risk of seeming paranoid. I did purchase it directly from Amazon so, in my mind, that makes counterfeit card less probable than defective original.Original review:I purchased this for my new Galaxy S8+. After purchasing, I transferred some large files to it and noticed it seemed to be going slower than advertised. I ran A1 SD bench on my phone multiple times which reported on average 14.25MB/s read and 19.12MB/s write. I hooked it up to my computer using a card reader and measured using CrystalDiskMark getting again, 15-20MB/s read and write speeds at best.Looking around the web for something to compare to, I came to a website made by Alik Griffin where he tests many different SD card speeds using the samsung galaxy s8. If his and my benchmarks are apples to apples, which they should be since we're using the same program and same phone, this card would be slower reading than any he tested, and faster at writing than only one other card which he recommends not to buy.This device does not meet the U3 specification which is minimum of 30MB/s write speed when tested on their newest phone. That being said, I had no issue recording 4k video with this card as the bitrate that the S8 records at is ~10MB/s. I would, however, like to have the advertised speeds for whenever I'm transferring files onto and off of the card. Maybe I got a dud? But what does that say about quality control...? I expect more from Samsung.