in my experience, the black pearl tends to grow several "stems" instead of single thick trunk. If you want to have a single trunk with a large crown, you will likely have to keep pruning off the suckers on the bottom portion of the stem. But it will be a cool looking Bonsai if you can get it to grow properly.
This photo kind of shows what I am talking about.

I agree....the Black Pearl really tends to produce side-shoots, rather than a single thick trunk. And it grows really slowly for me.

Josh

Isn't Bonsai all about trimming/guiding the plant into what you want?

This is my two year-old Black Pearl in her third season....she has decent shape, some good branches, too.

Josh

Color isn't bad, but not as deep as Pearls in year's past....

Last one, I promise....

Detail of the trunk and the prolific new growth of side-shoots.

Josh