When you buy a miner, what are you most concerned about?

[ajaxtempest]

Cannan do you use ESP 32 firmware for the nano and mini series?
https://unionrayo.com/en/bluetooth-chip-backdoor-esp32/

[NotFuzzyWarm]

Cannan do you use ESP 32 firmware for the nano and mini series?
https:// MALWARE LINK-esp32/

No they do not use that ridiculously under powered micro-controller & firmware...
They uses their own Kendryte AI chip and firmware same as their full size miners.

[philipma1957]

When mining at home, noise is important too. But generally speaking, most of this technical limits (noise, remote control, cooling, etc.) can be managed efficiently. 

Which means that ROI remains the most important in my opinion.

ROI depends on the cost of the machine with import taxes, its reliability, the cost of electricity, the evolution of the network's computing power, crypto value evolution for paying bills and your ability to use the heat produced).

Consequently, to have a chance of having a positive ROI, it is preferable to have low-cost electricity that is stable over time to make the machines profitable before they are outdated. 

You also have to be lucky (or well informed) to know if a new generation of chips will not make them obsolete quikely.

And if you don't have a lot of machines you also have to be lucky for it to be reliable... (If you have a lot you know that you will lose ~10% of your hashrate during first mounths burn-in)

if you are lucky you lose 10 of 100 miners in a small-medium  mine.

I have 4 s21xps 1 of 12 boards = dead.

I have 4 t21s issues with 3 of them

I am repasting them which seems to have worked.

[Crypt0Gore]

When mining at home, noise is important too. But generally speaking, most of this technical limits (noise, remote control, cooling, etc.) can be managed efficiently. 

Which means that ROI remains the most important in my opinion.

ROI depends on the cost of the machine with import taxes, its reliability, the cost of electricity, the evolution of the network's computing power, crypto value evolution for paying bills and your ability to use the heat produced).

Consequently, to have a chance of having a positive ROI, it is preferable to have low-cost electricity that is stable over time to make the machines profitable before they are outdated. 

You also have to be lucky (or well informed) to know if a new generation of chips will not make them obsolete quikely.

And if you don't have a lot of machines you also have to be lucky for it to be reliable... (If you have a lot you know that you will lose ~10% of your hashrate during first mounths burn-in)

if you are lucky you lose 10 of 100 miners in a small-medium  mine.

I have 4 s21xps 1 of 12 boards = dead.

I have 4 t21s issues with 3 of them

I am repasting them which seems to have worked.

Since you are focused on crypto mining I will like to know how you are cooling these machines, by air vent using fans or other cooling method? Because I heard that the more Asic miners you put side by side the likely they will have or develop some fault later, a single Asic miner installed in a well ventilated area will likely live longer than 10 Asic miners in the same spot getting cooled by air.

I think cooling is the problem that these Asic miners have, which is why I am looking into some home made BTC miners, they are more wider than S21 build style, which equals to enough space for air flow.