It's 30% failure in 3 months. How high can that go in 6 months, in 12 months, or in the expected life span of a Dell monitor?

Manufactured products tend to have two spikes in their failure rate: soon after being put into service (manufacturing defects showing up when the product has been used a bit) and near end of life (parts are wearing out due to long usage). In the middle, the failure rate is pretty flat.

Monitors failing within 3 months suggests that you're seeing the infant mortality part of the curve. If a particular monitor lasts 3 months, it will likely last for many years.

It's more of two slopes rather than two spikes:

https://en.wikipedia.org/wiki/Bathtub_curve

Tangentially related, but still interesting: most people think hard drives have a bathtub curve when failure rate is plotted against time. Turns out this isn't true.

Schroeder and Gibson: "Contrary to common and proposed models, hard drive failure rates don’t enter steady state after the first year of operation. Instead failure rates seem to steadily increase over time."

http://www.pdl.cmu.edu/PDL-FTP/Failure/CMU-PDL-06-111.pdf

It depends on how much you value the extra time and effort it takes to replace them. If you buy spares ahead of time to negate that time and effort, then have you really saved money?

The point is that a 30% failure rate is less than the 50% discount so you only end up saving 20%, with the spares included in the purchase.

But if 20-30% failed in the first few months of an expected 5+ year life cycle, that's indicative of a >50% failure rate in the medium to long term. You'll probably come out a loser in monitor-years/dollar.

That does not necessarily follow. See the "bathtub curve".

See also "time value of money" - if you don't have to buy the spares until they fail, all that extra money is worth something to you.

There is a reason Toyota and co don't have 6months of parts on hand - and it isn't due to shortage of shelf space