It is better to trust Brighton with the winning than giving it to Manchester United. Manchester United didn't conceive against Fulham and Brighton didn't conceive either against Everton. This is an indication that both teams are good defensively, judging by their games so far, so it would be best to play the bet under 2.5 goals. That's a more likely outcome, since both teams are boasting of a solid defense.
Manchester United are disappointing but I can neither go for Brighton. About under 2.5 goals bet, I do not think it is good to use just a single match to make such conclusion. At least, you should look for 3 to 5 matches between both clubs but the season has just started. I am not implying that you may not be right but a single match is not enough to make such conclusion. But if I still remember what happened in last season, it was hard to score more goals while playing with Manchester United.
Man United and Brighton both managed to get full points in the first week of this season. And actually I think both of them are quite trustworthy this season after a good start to the season. but I agree that we cannot reach any conclusions at this time considering that the season has just started and we cannot draw conclusions from just one or two matches. But for the Brighton vs Man United match, I think it will be a match that is quite difficult for us to predict the outcome. But I think both teams will score equally. but I'm not sure which team will win, whether the home team, namely Brighton, or the visiting team, namely Man United. And for me a draw is probably much more to be expected from this match.
For the both team winning their first league matches doesn't guarantee them a nice spot at the end of the season, we might even get to see them drop below because most teams are still working on their transfer window which causes a lot unstable performance untill then it's a whole pattern of luck on who wins their fixtures. The match between Manchester United and Brighton will be tough but more of the odds to favor United only if they will be more clinical when having those opportunities, last match played Bruno and Casemiro had good number of chances to score goals but where incompetent to raise the number, I hope they do better this time.