$300 is possibly the single most expensive pricing tier I have ever seen for a game.
You would have to play the game constantly for 3 years for it to even be worth it. I wonder if anybody actually buys it. You would really, really have to love Roblox.
5.95 for a month is a lot more reasonable. Chances are you'd only play the game for 1 or 2 months, then quit playing, then come back later, then quit, etc. It's by far the best deal. Flexible pricing and paying for what you use is better than even the 6 months or 12 month deals. Sure, you save a few bucks if you know you're going to play it constantly over that 6 months. But if you even don't play it for 1 or 2 months the savings are huge.
And out of that 300 deal the savings are more pronounced. It's almost guaranteed that you won't play the game at least a month out of that time and then the whole 3 year deal breaks down. If you skip even a couple of months it will take many years for the 300 to be worth it. If you're ten now, will you still be playing Roblox when you're 25? Probably not.
If I had a kid and they asked me to buy them the $300 Roblox I would do it and then never buy a single game for them ever again. Every time they asked for something else I would say "No, I paid $300 for Roblox, go play it." The savings on games would be pretty big, so it's a good deal for me.