This definitely depends on your situation.
If your furnace is relatively young it's probably not going to require major service anytime soon so you may not need it.
As sdg said, if you can tolerate a couple of days with no heat, you may not need it.
If you have access to trusted HVAC repairman, you may not need it.
Mind if I ask how much they're charging? There's definitely a pain threshold that will vary based on your needs.
For example, I'd be willing to pay up to $10. But that's mostly because of the annual maintenance check. If I had an older system or depended on it more, my pain threshold would be higher.
My local gas company offers this service for around $20/month. That's not worth it to me because I'm estimating (i.e. guessing) that any repairs I need to do in the next 5 years will cost less than 51220 = $1200.