I have read few stories of people being told to change the ECU because it is not powerfull or change to from 13 to 10 pin
Well when you change an ECU it should be the exact as the one one you are taking of with the same pins, pins are connections to car sensors and electronics, if you put a 10 pin instead of a 13 it means,3 sensors or electronics connections might not working and you wouldnt know, what will be affected in the long run or even when you just turn on the key

Every ECU is designed for specific if engine you change to more powerfull(replacing the weak one)how do you expect your engine to last long when the ECU is not designed for your engine, As long your mechanic has not pull a code from the ECU do not allow him/her to change the ECU, Only codes, physical damaged and corrupted ECU can force you to change, codes point where the problem is, then error link can be a corrupted, damaged or scanner being not compatible with your car model or make, a good techician will elimate all those to find the real problem, before asking you to change the ECU but not with one with less pins

This also covers the transmission brainbox

Remember when you change the ECU for the main car you need to also change the ignition key since the ECU stored the security code for the key, but some make and model have the 2 ECUs the main ECU one then one for Key Code, they work this way when you insert the key, the key ECU reads the code, then sends the signal to the main ECU then the car starts 307 peugeot has this system, if the 2nd key ECU (BSI unit) is corrupt your car wont start it affects the windows, central locking, and the radio

This is just basic of those brainbox

There are things like ECU remapping to increase horsepower, security code erasing(no need for the ECU to read the key chip to start) we did it on a peugeot 406 10 years ago, i dont know if it can be done now