considering OP has said "old router" I feel like it's a budget constraint thing.

I happen to like meshes, but only if the access points have wired backhauls. And even then, for a stationary setup like a desktop, you really don't get any advantage of using a mesh; the issue that meshes were designed to solve was the seamless transfer of devices from one access point to the next. Since the desktop is not likely to be moving throughout the house, there's no clear benefit, here, for a substantially greater cost.

A simple 5ghz connection might also work flawlessly but it all completely depends on what equipment he has and his house layout