First, he's a very solid addition to the many blue-oriented, artifact-love archetypes that see a ton of play at the kitchen table
LeFou himself is not a strong card, bu he can help you prepare cards with more Strength or abilities
Cheating on mana is arguably the most broken thing to do in Magic , and copying spells is basically that, so having a creature that can give you six or eight mana worth of free spells is no joke
not every card from the Commander Deck will make it to Arena, but every legendary creature of the Commander Deck will head there, and various bundles come with Mythic Turtles, special sleeves, and more
Theyre just there because theyre the right colors, and have the words roll one or more dice on them, although the card draw is a nice bonus