I'd put Holley drop-on harness quality a notch below OE. If I happened to get a deal on an engine that included one of their harnesses, I'd use it. But if I needed to build a harness from scratch for a project, here is what I'd do differently. Holley harnesses are definitely built to a price, and there are things you may find are worth spending extra for.
1. They use split convolute loom. I'm not sure if it's basic low temp stuff that will be crunchy and crumbly in a few years or if they've gone with higher temp, which is usually indicated by a gray stripe. I would use Techflex F6 for a basic street wiring harness - I once accidentally set an F6 wrapped harness on fire, and couldn't find the damage after the fire burned out.
2. I would use heat shrink tubing with cable ties to join sections of loom, instead of electrical tape. Looks better and holds up better.
3. Instead of unsealed relay sockets, I would use a sealed relay / fuse module like the Eaton RTRM series.
4. I'm not sure if they are using genuine OEM connectors or cheap knock-offs, but from their price point I would suspect they're cutting corners here. Real OE connectors have a pretty noticeable edge in fitment and the quality of crimps; I wouldn't cut corners there.
I haven't heard of Holley cutting corners in ways that are actually scary, like using cheap wire that melts from underhood heat. I'd call the Terminator harness an adequate harness that is built to a price.
