If you go beyond the 1 year mark, you no longer get the "free parts". From then on out you have to pay for parts and service, which can cost around $90. This is more than the service my wife pays for Poseidon regulators.
This has not happened to me. Due to travel, I've cut it close on the service in the past.
A friend of mine just had to pay over $90 for a Mk25/S600. So much for free parts.
This program sort of locks you in to the annual service, whether the reg needs it or not. If you miss it, you're then free to get it serviced at whatever interval you'd like. But it'll cost more.
I've brought my regs in for service even when the Intermediate pressure was fine, just to stay current with the free parts program.
Poseidon regulators have a 2 year service interval, my wife owns 4 of them. My friends new Scubapro cost is now higher than what my wife pays for her Poseidons.
As I'm buying more regulators, this is becoming more of an issue. I just bought a Dive Rite reg, in a couple of months I'll be getting a few more. I'll probably end up changing everything over to Dive Rite.
That being said, I love my Scuba Pro regs.
-Mitch