... for the purpose of being able to show the pictures just taken on a tablet, which takes microSD cards?
Are there any disadvantages to this approach one should be aware of?
The main disadvantages are:
In today's market, the first two points are typically less of an issue than in the past. If you have a compelling reason to use microSD, then I would say go for it.
Adapters can be produced very cheap, and they are. That gives the cheap ones larger mechanical (and possibly electrical) tolerances than typical SD cards. Anecdotically, I have a 5-pack of cheap adapters and some don't work in some readers while working in other readers/devices.
So it's likely advisable to use a brand-name adapter from a company that has the reputation and factory facilities for proper SD cards.