I do not think cashu is for holding. Is just a transport layer on top of LN to make it easier for poor noobs that can't afford managing a LN node (even a mobile one).

I would recommend reading these 2 guides:

1. https://darth-coin.github.io/beginner/getting-started-stack-sats-en.html

2. https://darthcoin.substack.com/p/bitcoin-adoption-using-ecash