The 704-piece Lego kit has no fancy special parts. It just has the old fashioned Lego bricks, plus a few plain bases and other items to help build some buildings, bridges, etc. It's a throwback to the original Lego kits of 50 yeasr ago where kid's imagination thrived. No TV characters, no Batman or other Super Heros, no pop culture stuff such as Elvis or The Beatles - nothing but Lego bricks, bricks, and more bricks. My grand nephews love it!
Yes, the more variety of Lego sets the better. I bought this set and another similar to it for the different style pieces. My granddaughters have enjoyed them and are building items without plans just for the fun of creating. They then take them apart and try other ideas.
Maybe it is a bit kiddie for a 12 year old though but....who knows it is Lego! Extra Lego bits are likely/always appreciated but Lego set that build something specific is likely more appropriate. Most of the DC comic line is very good Lego City and Star Wars are also sought after. It all depends on the kids interest.