I have worked with them on multiple jobs and thare guys are by far the nicest people (no attitude)
My opinion after only one experience with NSI is that they are crooks. Our building association (FirstService) recommended them to service the A/C in our condo. NSI gave us an estimate of $600-$1,000 to repair the problem. We called a different company to come give us an estimate...they replaced a $50 thermostat and everything has been working perfectly (total charges with trip, diagnosis, part, etc was $200). I understand diagnosis is never easy and expect a range, but 3-5X higher than the actual problem is unacceptable. Avoid NSI!!!
