B1 was obviously underpriced because it was announced around the time when the big 25% difficulty jump happened and nobody could have predicted the subsequent sub-10% difficulty increases.
Batch 1 was also fraught with initial production issues and stability, so the pricing actually isn't as good considering many get less than a stable 440GH/s, and B1 was initially advertised as being closer to ~480GHs.
Having said that, it's great to see that Bitmain has improved things with the newer batches. Would love to have some sort of trade-in program where I could return my wonky B1 S3's for the more recent ones.