Given the odds are x4.20 and x3.00:
Here’s my simple math.. if you bet $50 at x4.20, your total return is $210.
If you bet $50 at x3.00, your return is $150.
If you take the outside bet (even money), you bet $100 and your return is $200.
So, betting on the moneyline in sportsbook is actually less risky and more profitable.
If he bets $50 for each remaining game, as you mention, he would be risking the same $100, but with the variation that if:
1- If he wins the remaining two games, he would have a profit of $310.
2- If he wins the first and loses the second, he would have a profit of $110.
3- If he loses the first and wins the second, he would have a profit of $50.
4- If he loses both, he would have a loss of $100.
5- If he takes the bet offered to him, he can win $100 or lose $100.
Therefore, I wouldn't take that bet. The only advantage it offers is over game 2, which would win more. However, the other options give him a better profit margin.