Thanks for the explanation. I thought I couldn’t use that crypto with Ledger. Is it risky to use a 3rd party app for my ledger? If I'm using myetherwallet for example, I have to share my private key with them, isn’t it? If it is, I guess that's risky.
No, your private-keys never leave the device, which is the entire point of a hardware wallet.
All MyEtherWallet or other wallets will do is ask Ledger to sign a transaction, and then you can say yes or no.