I have a 1 TB Surface Book 2 that I have a 512 GB Samsung Evo Select (Amazon version of Evo Plus - got a good deal + less likely to get a fake because more niche branding) MicroSD permanently installed in (via BaseQi adapter) for extra storage. I haven't had a high-end MicroSD card fail in several years (aside from a fake be very wary of close fakes in this space, even sold directly by Amazon and such). SD cards (and USB flash drives, etc.) are generally made from low-grade flash, so endurance is also poorer - but as long as you don't store mission critical data on there without backups, it's fine. It'll work fine, but keep in mind the drastic performance difference between a modern NVMe SSD (pushing at least 1,000 MB/s peak read/write - and many can do 3x or more than that) and a MicroSD card (the fastest ones can deliver around 100 MB/s - slower than a mechanical hard drive). Has anyone used this set-up for any extended amount of time? Did you have any problems? With the SP7 I'm planning on a "install and forget" approach.
I've pretty much always been using MicroSD cards on my phones and had trouble with them becoming corrupted after a while - But these were also relatively frequently taken out and moved back in to the phones, which may have contributed. I think the 128GB ought to be enough for installing all the apps I need, so the additional 512GB would go entirely to file storage. Class 10 U3 cards have pretty decent read/write speeds, but I have no idea how that compares to an actual harddrive. So I'm considering getting a min-spec SP7 and extending the 128gb of storage by spending an additional 100 or so on a 512 GB MicroSD card. I'd like to get my hands on a surface pro, but the prices for anything other than the base models are really crazy, especially since the prices here in Europe seem to be a roundabout 200€ slapped on top of the (already high enough) US pricing, just because.