I would recommend a proportional thermostat (such as a Herpstat) for your incubator in order to provide more stable temps. Also the service life of a proportional thermostat is longer than a ON/OFF type since there are no parts "rubbing" to wear out, as ON/OFF types utilize a mechanical switch.
If you do decided to go with a ON/OFF type thermostat for your incubator I recommend checking out the RBI Vivarium Electronics VE-100 as it has a detachable probe and has no 'clicking' sounds when it turns on and off, which after awhile can drive you crazy.
The VE-100 is only 5 bucks more than a pre-wired Johnson and has a bunch more features, along with Rich from RBI's world class support.
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