How can I start with a core wallet quick simple and safe?

Hello There, I downloaded and installed the NanoWallet for Windows64bit because The NEM NanoWallet is the officially supported client. And I want to own the private keys of my XEM. So I started a Simple wallet on the mainnetwork (Mainnet) then I’ve got a notification. " Please read about dangers that client side generated keys pose… It’s still recommended to use a private key generated from a NEM client" So now I’m confused cause if The NEM NanoWallet is the officially supported client I would think that should be the most save one. Now I’m thinking I’ve should started with the NEM Client (NCC). So I followed the link to read about the dangers that gave me a pop-up message “This version is outdated!” for the latest version look at https://www.w3.org/TR/WebCryptoAPI/ So I don’t know any more Should I start with the NEM Client (NCC) or is the NanoWallet the most save to use now? I’ve allready created a private key for my simple wallet and made a backup. Should I not use that and instead install a NEM client (NCC) and create a new private key to use that instead of Nano wallet? For now I just want to buy and hold in a some XEM in my wallet and own the private key. Can somebody please make this clear?

Explanation are here CONFUSING: Is it better to use the nanowallet or the NCC?
It’s about entropy available to generate keys.
Personally I used nano wallet for generating simple wallet and it’s safe option in my opinion.