The difference is that Apple has developed something of its own, an SSD that only works within the Mac world. And Apple doesn't sell a bigger SSD after the fact.

The Transcend is specially made by a third-party manufacturer to be used in a MacBookAir or Pro. (Procedure: Unscrew notebook, remove old SSD and install the faster Transcend. Done.) In most cases, there is much more space on the new SSD. The performance is better.

The Samsung 980Pro, on the other hand, is not made to be installed so easily in a Mac. It usually has to be connected externally via a cable. That is certainly possible. The data speed is then limited by the USB connection. A disadvantage, it is fast enough, but clearly slower than a built-in SSD.
Another disadvantage is that there is still something attached to the Mac Pro. Cable clutter. More cumbersome for mobile use.

P.S.: There are different Transcend variants for the various Mac models of the respective manufacturing years. Important: Check exactly what you need for your MacPro.

because it is tested and fits (pin assignment, size) and works flawlessly in my macbook set purchase! I sent back several cheaper ones at that time!!!!!

If I remember correctly, the connector is different. Check the specs carefully for use in older Mac...