Is m.2 SSD worth the extra $?

Solution
The M.2 version is still SATA-based, so unless you need to save space from not having a 2.5" drive, no.

Full NVMe drives are around 4x faster (via PCI-E 3.0), but they're expensive, and somewhat limited by their form factor (have a look at U.2 instead - essentially an M.2 drive in 2.5" form-factor). Having said that, most/all modern SSDs are probably fast enough, anyway ...
The M.2 version is still SATA-based, so unless you need to save space from not having a 2.5" drive, no.

Full NVMe drives are around 4x faster (via PCI-E 3.0), but they're expensive, and somewhat limited by their form factor (have a look at U.2 instead - essentially an M.2 drive in 2.5" form-factor). Having said that, most/all modern SSDs are probably fast enough, anyway ...
 
Solution
The M.2 in reviews has shown to be barely faster than the 2.5" sata version. Barely as in only in .02 milliseconds, so you'll never notice the difference. Go with whichever is cheaper unless the physical space of a 2.5" drive is an issue.