@leriak I reckon it would be cheaper for you than for my DS1520+, but even mine was cheaper than a ... I was going to say Raspberry Pi 4 kit but I just looked and they are going for silly money on Amazon and UK distributors they say the lead time is > 1 year.
I agree on not usually buying extended warranties, and my other Synology NAS are still problem free... but they were cheaper to start with.
@fredbert It was 72.59€ (59.99€ + vat)... it seems to be in the same ballpark as your 1520+.
I got the nas from an official distributor which covered themselves directly the (legally required) 2 years warranty, usually retailers cover only the 1st year themselves. With proof of purchase, the extended warrany covers an additional 3 years from synology.
As with all warranties/insurance it's a good deal if you end up having problems, but I have to say that kudos to synology for at least allowing customers to have 5 years warranty on something that in the end is a consumer product, this is not common and needs to be commended.
Personally I think getting 4/5y (depending on the model series) is great like you said, from a customer perspective. That extended warranty for a 24/7 device that covers so many potential roles and TB of data is practically nothing.