There isn't a keeper that I've seen in the modern world of football that is amazing at crosses. Almost everyone of them flaps at them because there is more attention paid to blocking off the keeper than there used to be. That said comparative to his contemporaries he is pretty good really. The goal yesterday was less his fault than the defenders.
I feel more confident in his cross catching than I did with Pepe to be fair. Pepe was better at punching though, so swings n roundabouts.
Whatever comparisons made, which is natural for us fans, both were are very good goalkeepers for us so far. Personally I feel more confident with Mignolet in the sticks than Pepe (of the last few years at least).