After having problems with both my HVAC unit and furnace, I opted to get the Reliance monthly protection plan, which includes annual maintenance for both units, following good service after calling them out for an issue. I've had the plan for a few years and every one of the techs that comes out has been professional and within the confirmed time range. Only one has tried to up-sell me on a new system and he didn't push it when I declined.
The reason for the lower score is because of the customer service over the phone. For one thing, giving your phone number to Reliance will ensure that every month (or more frequently) without fail, you will be phoned by Reliance to ask how old your furnace is. Even if you tell them the first time, they will phone back the next month to confirm that your furnace is aging at the same speed as everything else on this planet. No amount of begging or pleading will get you off this list. Believe me, I have tried. They always say I'm off the list but the very next month they're back at it again. In the end I have just blocked the number.
Second, and less annoyingly, is that often when I call to make an appointment the customer service rep seems confused as to why the previous appointment only looked at one system. I prefer to have maintenance for the furnace before the winter and the HVAC before the summer, but this sometimes causes no end of confusion. It's always been worked out, but surely I can't be the only person who does this.
Overall I've been satisfied with the service, but my interactions on the phone could be a lot better.