I've cut and installed dozen of counter tops and never once used a router to make the cuts.
Any I've cut the tops where cut from the backside using a ciruler saw.
Nothing special about those IKEA tops there's still particle board on the back side.
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And I did one a week back WITH a backsplash, turned it upside down and just cut off what was needed with a circular saw.....but that end was going against a wall, not in plain site as part of a 25" long joint between two counters. Given the overall expense and pain in the whatevers of doing a kitchen, why even mess around? Go to a countertop shop....and for very little more get a quality product that will look good, fit, and last. Ron