Is an in-tank fuel pump really quieter and more reliable than an external one?

Generally yes, for three reasons:

• Cooling and lubrication: the pump sits in fuel, which keeps it cool and lubricated. That's a big reason OEMs use in-tank pumps.
• Noise: the fuel and the tank muffle the pump. External pumps can buzz loudly, which gets old on a street car.
• Protection and feed: an in-tank pump is always submerged and protected from road debris. An external electric pump has to be mounted low, below the tank, because electric pumps push fuel well but don't like lifting it.

In-tank modules also simplify plumbing: you get clean fittings for supply, return and vent. The trade-off is service — once it's in the tank it's harder to reach, so assemble it carefully (clamp the internal hose, insulate the terminals). More in best fuel pump for an LS swap.