No risk of losing cards. But I don't recommend using it on any account which you actively use for posting/voting. Because you give them your posting key, and basically, that's the most damage a posting key can do, if misused: posting or voting with your account.
No financial transactions. No card or other Splinterlands asset transactions.
PS: After HF26, I also don't recommend having HP in such accounts, to avoid any temptations. Only RCs.