I too would not suggest either for an incubator. Both have not very accurate probes incubators need accurate temps. Both J and R have a 2º+/- error range. This is too inaccurate for a incubator. That means you would need to add an accurate thermometer better than off the shelf ones. That means adding more cash, I would think at least one accurate to 1ºF or better and certified accurate (traceable) Ones that fit this bill run in the hundreds of dollars. In fact you could save some cash by using something like say a herpstat as they are less than a good thermometer and have this kind of accuracy. This is a reason to buy a proportional as most (in N america anyway) have less than one degree error. IMO a J or R can be used but only in conjunction with an accurate thermometer.

It is like buying a sports car because you got a good deal on the tires.