I've been using CrystalDiskMark for some time now. Seems to be pretty reliable. I get fairly close to advertised speeds on my drives, but you have to consider makers post those speed ratings for sequential reads and writes with everything optimized. If I get close to that with CrystalDisk's sequential read and write test I'm happy. That's the test at the top, yields the highest results. BTW, you can see disk transfer speeds in File Explorer when copying files by selecting more info. I haven't found that to be a very reliable indicator of disk performance. Even when using a single large file disk to disk, it's always a lower speed than what I see in CrystalDisk. I tend to think that indicator in File Explorer is not very accurate. I've seen inaccuracies like that in File Explorer before. For example, right click on the system disk and check usage. Then show hidden and system files, highlight all folders and files, right click, and check disk usage that way. The numbers are greatly different. And it's not the way you expect either, disk usage comes out greatly higher when highlighting and right clicking all folders and files
My only objection to the tool is that it sometimes gives different stats for the same SSD when run more than twice.