In terms of speeds yeah, there won't be any big improvement same way even using a Sandisk Extreme is worse than the Ultra because Switch doesn't support the faster format, its just compatible, but doesn't use the full speed of the extreme making it a very bad option for a M-SD as its quite a lot more expensive than the Ultra and on a test on youtube, the Ultra was even faster loading games though for like a second...
In terms of space SSD is still a lot limited and not much cheaper than an actual SD card depending on the GB... a 120 to 128 GB SSD with older Sata III interface here is around 40€ and the 128GB M-SD Sandisk A1 Ultra is also ~40€.
Only a HDD would be a cool option in terms of capacity per price, though I don't think the SD port will be able to output that power maybe it would need to be powered by a external power bank to work, we most likely needed to buy a internal 2.5 HDD and buy a case with power input (some have separated power for more demanding hardware). Most power banks have multiple ports so it can power the HDD and the console at the same time and give HUGE play time specially a 20A power bank with Power Delivery from 5 to atleast 15V with multiple port outputs.
But we still need someone making some adapter from M-SD to USB...