Fedimints / eCash are very interesting and are great tools. Particularly great for onboarding and for payment networks connecting various vendors as it improves the privacy significantly over a SQL database from a single custodian.

However, the biggest area of concern is potential for Fractional Reserve debasement (see: https://fedimint.org/docs/TradeOffs/DebasementRisk) (Note this exist as well in SQL database scenario, so no increase of threat there)

While the BTC held can't be debased, the eCash issued can be. There are strategies that could mitigate that, like software clients that perform coordinated bank runs in an automated fashion, etc.

However, there are also conceptual approaches that you can use to protect yourself: namely, sizing your exposure.

Often in these discussions we take a "one size fits all" approach and ignore the reality that any transaction - of any sort - have counterparty risks (ie. you bought a book from a vendor and they don't ship your book).

Consider the following allocation:

At any time you can swap more LN for eCash (if you needed to make a bigger purchase)...or vice versa you could cashout of eCash totally if you have no pressing need to make purchases.

Likewise as you build-up LN reserves, you could periodically move to BTC as fees permit.

In effect, eCash should be used only as a transactional coin and shouldn't really be held for any significant length of time.

Fedimints / eCash are a solution layer that handles the "last mile" problem (onboarding and payment networks).