Hi, thanks for your reply. Yes I believe it is safe, there are many people who use them here on Steem and they haven't reported anything. I myself use it once in a while, though replying like this long, I prefer to use my desktop.

For SteemMonsters, there is an initial cash layout of $10USD to buy your "starter deck" but that's it. You can use that deck to play the game and earn cards as rewards. You can use those cards to beef up your deck or sell them in the marketplace for Steem.

You can get Steem Power by powering up from STEEM, which you can get basically by 1) buying STEEM from crypto exchanges and/or 2) creating content and get rewarded with Steem Power 3) if you have enough Steem Power, you can earn more by upvoting content

For the last one, I just started with it but what I do is the data entry, I don't want those installing apps and playing games as I only play Steem Monsters.

Hope this helps