Plaid really do seem a little dodgy to me. In the UK they are effectively offering a PSD2-API forwarding service, which seems very much against the spirit of PSD2 and the open banking initiatives.
It's very convenient. But also very expensive (maybe)
The raw costs of getting an AISP licence are about £1000 in the UK... but that's ignoring all of the time and effort to understand PDS2, legals etc but $500+/month for Plaid to do it for you ? I'm not sure. Sounds avoidable like vendor lock in to me.
Plaid is mainly US where PSD2 does not apply. Banks sometimes get together to work on these topics but it rarely goes well (see ofx/ofc). What more frequently happens is a company like Plaid forces it and then works with banks to satandardize.