The B. smithi was one of the first species on the scene of the tarantula hobby and it does not dissappoint. The "True Smithi" used to be anitha and is similar to the other species known as the "Mexican Red Knee": the B. hamorii.
These 2 species were seemingly one species that became seperated by a river in Mexico causing them to diverge and form two different species that are similar but have slightly different characteristics.
B. smithi does appear to get a tad larger and more red and so over the years it has been more popular by enthusiasts. It is also harder to find becuase for years, hobbyist would cross breed these two similar species together unknowingly due to them being so similar.