The initial price is similar, but they use dramatically different amounts of power, ~10x more. If you're capturing the heat for something useful maybe it makes more sense.
S9 14TH/s @ 1400W
BitAxe 1.4 TH/s @ 15W
Discussion
Is the S9 also 10x more likely to find a block? Seems like as long as it’s being used for heat too that is an efficient option.
10x more power per TH/s. A single S9 vs a single bitaxe is more like 95x more power usage, but the S9 gives 10x TH/s.
The bitaxe uses a newer, more efficient asic, that's all.