"well designed" depends on your goals and use case
Major downsides of Ecash is that the underlying asset is custodial and Ecash reintroduces seigniorage (mints can print ecash on a whim). Bitcoins only major value props are destroyed. You bringing back trust and custodians.
With Monero you can have privacy without sacrificing custody or seigniorage
Ecash is also not exclusive to Bitcoin. You can have Ecash on Monero. It's just an IOU.
