I would not be surprised if one day I see you complain that your funds are stolen because you downloaded some file from some website. How convenient it must be for hackers that someone would actually use their work and hand their private keys.
And its much secured if you make different wallet to eth and btc there is no reason for you to use the same private key from different address?
Its much easier to make a wallet and stored your keys to safe place , than give your to trust to unknown website that claiming they can make you both eth and btc address with the same private key.