The Switch 2 comes with 256GB of internal memory, so it may not seem worthwhile to add only 128GB of external storage, but some is better than none. microSD Express is significantly more expensive than a standard microSD, and the best option is always the option you can afford. This is likely going to be the most popular choice for storage on the Switch 2.
It doubles the usable storage of your console, and at $60 it isn't an outrageous price either. If you're a hardcore gamer and you think you'll have dozens of games loaded onto your Switch 2, then you may want to go bigger, but I think for the average person, a combined storage of 512GB should be plenty. While the Switch 2 can technically use up to 2TB microSD cards, those are few and far between.
We did manage to find this 1TB card that fits the microSD Express criteria, but it is not a cheap buy. $200 for 1TB of extra space is a lot, especially for a handheld that will cost $450 already..
Technology
The Switch 2 Is Almost Here and You Need a Specific Type of MicroSD Card – Here's Where to Find Them

The Switch 2 will work only with microSD Express cards, so it's likely your old Switch card won't do the trick. We've found all the places where you can pick up a new one before the launch.