For incontinence, the stimulator must accept an internal probe and have parameters designed for the pelvic floor; a generic TENS with skin electrodes does not do the same job. Pressure biofeedback shows the patient a contraction they cannot feel yet, and it is what makes the home program work.
Probes, cones and tips are single-patient use: they belong in the cost per patient, not in the price of the device. Check the price of a spare probe before choosing the brand, because that is what you will buy again for every new patient.