The ROI is the most important.
I look at how long it takes for the machine to produce what it cost me. Now, if it's more than 9 months, I don't buy.
Several of my latest machines did not produce the BTC they cost me. Because of the low reliability of bitmain machines, the increase in difficulty, plus import taxes, it's hard.
If a machine that costs 0.1BTC only produces in it's working life 0.08BTC, there is no reason to buy it, it is better to keep the money.
I don't know how other miners do it, but for me in Europe it's no longer profitable, even with free electricity.
I agree ROI is important. The home mining price needs to come down. I was seriously considering buying the mini3 when it was launched but the price point is so high. $899 for the miner + something like $120 for shipping. It would take something like 18 months before I got my sats back, and that assuming difficulty doesn't go up during that time.
price point for home miners needs to be below $600 for units like the mini 3