Incorrectly set thermistor can show you +30C more than it is, you will force extrusion, and bam hot end damage or stuff like that.
That is to say, if you skip messing with thermistor, in the end thermistor will be messing with you. Your choice. :)
Afaik there is no default, but i think first used were 100k, and that or 200k even are probably better at high temps. Its rating better be 300+C, the one with 250C i wouldnt trust.
And 20% tolerance means that you have a thermocouple ready to calibrate its thermistor table, otherwise its useless. If you dont have means to read real temperature then you cant customize it, then you are better with something aiming to 0.1% tolerance which is gonna be more expensive. But if you have a thermocouple you customize your own thermistor table and that should be best thing to do either way, and only then you can use something like +/-20%, since you customize it then doesnt matter what error it has from the rest of its batch.
First of your links i believe points to a product series that was widely used for reprap before, but i think with 100k value.
That is to say, if you skip messing with thermistor, in the end thermistor will be messing with you. Your choice. :)
Afaik there is no default, but i think first used were 100k, and that or 200k even are probably better at high temps. Its rating better be 300+C, the one with 250C i wouldnt trust.
And 20% tolerance means that you have a thermocouple ready to calibrate its thermistor table, otherwise its useless. If you dont have means to read real temperature then you cant customize it, then you are better with something aiming to 0.1% tolerance which is gonna be more expensive. But if you have a thermocouple you customize your own thermistor table and that should be best thing to do either way, and only then you can use something like +/-20%, since you customize it then doesnt matter what error it has from the rest of its batch.
First of your links i believe points to a product series that was widely used for reprap before, but i think with 100k value.