The download link is benign and with say Firefox in desktop mode you can download the game, which is also what it claims to be (and quite fun!). Still wouldn't recommend using the download manager.
MEGA is popular, yes. Well-known? Depends on who you ask. Trustworthy? God no. Maybe years ago. Just reading the first few google hits should give you the creeps. A download manager gets full storage and network access, which basically means they can upload your photos to the internet if they want. Definitely not qualifying for that level of trust.