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No, it's illegal to say 'the use of' compatibles will invalidate a printer warranty.
On a rare occasion that something ever went wrong, a standard printer warranty (the 12-month one you get when the printer is new) can not be invalidated. Printer manufacturers can sometimes be funny with extended warranties (one bought separately from the printer or an extended one after 12 months) but we cover your printer with our compatible guarantee too so we would fix or replace your printer if a compatible caused it to stop working.
It's extremely rare, I've worked here 13 years and only seen it happen a handful of times from hundreds of thousands of orders! If you have any more questions, let me know!