I have bought both the SanDisk 500GB Extreme (550 MB/s) and the SanDisk 500GB Extreme PRO (1050 MB/s) to use them primarily as external drives for my iPad Pro 12.9” 3rd Gen.Both drives are great and and work flawlessly with my iPad Pro using iPadOS 13 file system. What follows is a side by side comparison between the two SanDisk drives.Weight and Size: The Pro is much larger and heavier than the Standard (77g vs 40.7g ). BTW, the cable that comes with the Standard model is too short to rest the drive on any surface. Thank god, the SSD is light enough to safely dangle by the cable off the iPad.Temperature: The Pro remained cool even during writing a 95GB file to it for more than 25 minutes, whereas the Standard model was very warm to touch after writing to it a 5GB for less than 2 minutes. No wonder, additional 37 grams of aluminum body on the Pro absorb and dissipate heat faster. Solution: Don’t copy giant files to the plastic drive unless the ambient air is cool or point a small portable fan at it.Protection against the elements and overheating in hot and humid climates:Both drives are rugged and will probably withstand hot and humid environments, like Costa Rica where I live part of the year. The Pro will run cooler under the same circumstances.Price: The Pro is $125 whereas the Standard model is $90, minus 15% cash back special, so the effective price is $76.50. It is almost $50 less than the Pro. The Pro is new this year. The prices may come down in 2020.Performance: Note that iPad Pro supports the true USB 3.1 Gen 2 interface, that allows the Pro to reach it’s maximum transfer speed of 1050MB/s, as per product description.- Copy ~5GB file from the SanDisk to iPad: Pro - 22 sec, Standard - 45s- Copy ~5GB file from iPad to the SanDisk: Pro - 67 sec, Standard - 106s Here the Pro is almost 2x as fast in both directions.- Copy ~95GB file from the SanDisk to iPad: Pro - 10m 50s, Standard 10m 39s (Here there is no difference, probably because the write to iPad speed is the determining factor, not the read from Sandisk)- Copy ~95GB file from iPad to the SanDisk: Pro - 26m 15s, Standard 37min (Here the Pro is about 11 minutes or 40% faster than the Standard).The only real performance advantage of the Pro model is when copying giant amounts of data (hundreds of Gigabytes) to the SSD from iPad. I am willing to wait extra 10 minutes for every 100GB to save $50.Copying large amounts of data to iPad from both SSD’s produce identical speed.On my 5 year old PC with USB 3.0 interface, the time writing the 95GB file to either drive was identical - 5m 20s at 290MB/sec.(Note that the PC with USB 3.0 is 5 times faster writing to the Pro SSD than iPad with USB 3.1, and 7 times faster writing to the Standard than iPad. I guess iPad Pro is not very good at writing to external media in general. Can it be that Apple intentionally slowed the Write to external memory API, to sell iPads and iPhones with larger built in storage? Mine is 256GB.)Bottom line: The small speed/time advantage of the Pro in most real life situations, like editing video files on iPad and then saving the results back to the external SSD, does not justify IMHO almost double the cost of the Pro compared to the standard model.So I kept the Standard model and the PRO went back to Amazon.Both drives deserve 5 stars and both have their own advantages for different types of users.UPDATE for tech minded:As per some users’ advice I reformatted the drive. Changed the exFat Allocation Unit (AU) or Cluster Size from the original 1MB to the Microsoft’s default of 128KB (8 times smaller). To change the AUS or cluster size do Quick Format only. You will still lose all the files on the drive.This saves about 10% of space for my large collection of MP3 music files which average 1 to 5 MB is size. For video files that are 1 to 5 GB it does not matter. For large number of word documents, TXT or HTML files that average less than 128K, the space savings can be 90%.The small AUS slowed the data transfer speed from 2 to 8 times depending on configuration. The worst case scenario is on PC. Copying the huge 95GB file to the Standard Model SSD went from 5 to 40 minutes. The slowdown makes sense because the each cluster is transferred as a single read write operation. The total number of clusters transferred increased as the cluster size decreased about the same 8x. Bottom line: Use AUS that is appropriate for the typical file size in your application. What you save on space will come out of the speed. exFat for allows clusters as small as 32K.