There is no difference between the 450 gem option, compared to buying three heroes using the 150 gems option.
The percentages of acquiring a Legendary hero is the same.
He is pretty neat because he is very tanky with a lot of health. If you have a big group of troops behind him you can smash through bases. I like him a lot. He is also cool for arena to use as a meatshield for a squishy caster.