About Electrs vs Fulcrum servers ...

These are both Electrum SERVERS. An electrum server is different to a wallet, and a common cause of confusion because of terrible naming.

The purpose of the Electrum Bitcoin is to keep a copy of the Bitcoin blocks in an alternative structure to better serve as a backend to a wallet (Electrum Wallet must have an Electrum server, but Sparrow can use it or not).

Your wallet can then EFFICIENTLY ask questions to the server about its balances. The Bitcoin blockchain is not optimised for this, it is optimised for unstoppable, uncensorable, immutable money (and apparently Monkey JPEGs).

When not using an Electrum server, as Sparrow Wallet can do, and also Specter and others - the Bitcoin client creates a Bitcoin wallet in clear text of the connecting wallet. So if you open Bitcoin QT, it shows the balance, not good for privacy. Like I said, not optimised to be a wallet. It also communicates to the wallet via TCP, not SSL, so traffic is not encrypted (IDK if this has changed recently)

Electrs (Electrum server in Rust, Rust is a nanny programming language) is very stable, and it's rare for the database to be corrupted.

Fulcrum is FAST, way faster than Electrs and even Electrum X, but the database FREQUENTLY gets corrupted, necessitating a complete resync -- annoying.

For ParmaDrives and ParmanodLs, I ship these with Electrs as the backend, even though Fulcrum is the fastest because of stability.

I'm thinking now to ship them with BOTH electrs and Fulcrum synced. Use Fulcrum, and if it craps its pants, sorry, WHEN it craps its pants, the slower and more reliable electrs is there while you resync Fulcrum.