they are both k type thermocouples which will cover the roasting temperature range just fine. thermocouples are made by using two dissimilar metals which create the thermoelectric effect that can be used to measure temperature. So the composition is the same.
All thermocouples are going to vary from unit to unit ever to slightly so it is best to calibrate them before hand. The best calibrator is water! ice in a funnel that is melting will have water that is precisely 0 deg C! similarly water that is on boiling will be at 100 deg C. Assuming close to sea level :)
Either part will be fine, get the cheapest one! just make sure the cable is long enough for your needs. You mentioned you already have a adapter for your DMM so you wil be fine to order them with regular thermocouple connectors.
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