The problem with warranties these days is they are setup to simply replace the hardware, and not provide quality hardware in the first place.
Things I've noticed, most places which offer a third-party warranty will ensure the process for obtaining the warranty benefits is difficult and onerous, where it might take several months to get the replacement, and in the meantime you have no laptop, and then they only replace it with a like-model which may have the same problem, they'll do this multiple times for the length of the warranty, after which you'll almost certainly need to replace the device, while accounting for periods of time that you may not have the device. Unfortunately, many manufacturers have gone this route as well in recent years offering a 1 year manufacturers warranty and then 2-3 year support warranty. You used to be able to get business class laptops with a 3 year manufacturer warranty and it was manufactured so it wouldn't fail in that time (with quality components).
You'll have to decide what amount of risk you are willing to take. A new device is a lot easier argument to enforce a warranty, you'll still run into the issues with delays on the process if it fails, but there may be other tradeoffs for your use, you'll have to decide.
Coreboot also doesn't support the T480, looks like the T440P was the last model they support, but I could be wrong on that.As always do your due dilligence.