I looked at a prefab build recently for someone I know, and the quality honestly surprised me - the joinery was tighter than most site-built houses I've seen. The factory environment really does eliminate a ton of variables. You're not dealing with crews working in rain, materials sitting exposed for weeks, or inspectors having to sign off on rushed framing. Labor shortages have pushed this forward too; modular plants are staffed, whereas finding reliable crews for traditional builds is a nightmare in most regions right now.
The cost difference is real but not always what people think. You save maybe 10-20% on labor and some material waste, but that gets smaller once you factor in customization, lot prep, and getting units to your site. The speed advantage is where the money actually lives - 6-8 months from contract to keys instead of 12-18, which means you're not carrying financing costs as long. That matters way more than people realize.
One thing nobody talks about: check your local jurisdictions before you commit. Some towns have outdated codes that don't play well with modular certifications, and you can end up stuck waiting for variances or paying extra for on-site inspection. Call your building department first, not last. Also, if you're financing, make sure your lender handles modular - some banks still treat them differently, which can affect rates. The homes themselves are solid, but the ecosystem around them is way less standardized than traditional construction.