The site is called MEGA and is a well known download site. The "dubious" download manager is there to help prevent broken downloads which happen quite often with bigger files esp. on mobile.
If you get redirected to any other site, then you might want to check your phones security settings and or change the browser.
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.
Well if you had my internet connection you'd want to upload as less as possible, because it simply takes ages and since itch isn't the only site where I upload the games I have to chose a reliable upload service and so far mega didn't disappoint + it give you the full download speed.
Thanks for playing the game though, let's hope I'll get better internet soon^^
