I also don't like the idea of typing your recovery seed into a website because you want to get the right private key for a particular address or others, since this website works online I don't recommend using the same wallet for storing funds anymore, typing your keys online is already a red flag for me.
You do not have to trust using online site for seed phrase generation or to know which key belongs to an address using iancoleman, you can just make use of the html file offline.
https://github.com/iancoleman/bip39/releases/tag/0.5.4