Character Summoner

The only thing to keep in mind in character summoning is that the rates for 4* heroes are at a horribly low 4%. People can buy huge amounts of gems and do the "10 Summons" all they want but it is most likely they will get mainly 2* or 3* characters along with duplicates.
That being said the player will also receive unique runes from duplicate characters that can be used to help advance the stats of whichever character they wish. Like mentioned in the game, there is no guarantee a player will obtain a specific character of their liking, most of the time it would be a completely unexpected or random character.