I would be willing to say those units could under clock to 18watts a th
They sure would, but would be adding a large number to the cost per th, I like to compare mining gears based on their labeled specs, I am sure the S19 XP too can probably do 18w/th with some underclock settings, default settings are what matters to me, MicroBT has an edge over Antminer which is the quality, the XP is better than the M50s++ in terms of delivery, it's today vs 5 months wait.
To me, the longevity of the gear is the most important aspect, I rather have a gear that is set to ROI in 10 months knowing that it would likely run for 30 months without issues, than a gear that could ROI in 6 months knowing that it will hardly run for 10 months, but all of that depends on your plan, power bill, access to the factory warranty, ability to fix your own hashboards and a dozen more reasons.
my model is simple, I have free and limited power, and I want to squeeze the most hashrate I can without having to pay the highest $/th, so I don't buy the newest models or else what's the point of having free power? I also don't want to buy old gears that will fill my farm without any considerable hashrate, this forces me to pick mining gears that can live for long since that's all I worry about, I make a profit as long as the gear is alive regardless.
Of course, someone else who pays a lot for power might be looking for other things, efficiency could be everything they care about, it's hard to assume what other people are thinking.
