It's the fastest SSD on the consumer market by a good margin. My main gripe with it is that Apple doesn't provide any affordable option for large, slow storage. Of course you can always go external, but then it won't be so much mini anymore.
Except... it's not. We know that larger SSDs are faster... but if we compare a 1TB Apple SSD in the iMac Pro to a 500GB 970 EVO (around $120)... the 970 EVO is at least equal, if not faster in performance.