You do get mox opal only hands you have to mulligan, but overall the mulliganing isn't too bad. It is better than something like blue belcher, as at least you have lands. As @ChubbyRain says, the problems are the vulnerability to artifact mana disruption and sometimes the lack of color fixing. There is a tension between turning on mox opal, having access to colors, not having too many mana sources total, losing to null rod, and not playing mediocre cards just because they are artifacts.
I definitely got better than average draws throughout the tournament and avoided null rod/stoney silence/kataki etc.