sendfrom "account" or sendtoaddress. This funcions are safe to use it ?
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All the functions are "safe" as long as you know what you are doing and you use them properly.
Most functions are not "safe" if you don't know what you are doing and you use them incorrectly.
"sendfrom account" Will create a transaction and will update the account balance for that account. You can not count on it only using transaction outputs that were received associated with that account.
"sendtoaddress" will create a transaction and (if I recall correctly) will update the default account on the wallet. (I might be mistaken on that. It might not update any account at all. I'm not confident in my answer and you may want to wait for additional responses from someone more knowledgable than me on the "sendtoaddress" function).
Generally, I would advice that you create your own account system outside the wallet. Use the wallet only for creating transactions, and for notifications about transactions and/or blocks. You have very limited control over the accounts in the wallet, and if you create your own account system, you'll be better positioned to handle activity in the way that you want it handled.