A key piece of the Simic package when it works is card draw, which you can see when you look at the most popular Simic commanders at the top of this list
This card gains ATK equal to that equipped monster's
It introduces special guests, which are highly desired reprints that match to the world and flavor of the world they appear in
Another change that players are excited about is a new round of Item cards that could shake up competitive TCG play
The main issue with Command the Dreadhorde is that it costs the same as Bolass Citadel, so I think you basically need to choose one to play (though you could sideboard the other) and I believe Citadel is likely to be better, as all it requires is a lot of life, as opposed to a lot of life and previous setup
Within the first three set types the amount is mostly consistent (with some exceptions), while for Special Expansions the amount varies