Seater is the big difference, and shell holders... Hornady seater is very good and handles different cartridges of the same caliber...ie 308 seater is identical between 30/30, 7.5x55, and a few others. They are a better seater then the Lee set up, and wayyy better then the standard RCBS seater. Benchrest quality almost...in my experience anyway. I've had quite a few off center Lee shell holders, enough that I don't trust them at all anymore. Probably why they include them free... Hornady I've had no issues.
I still like Lee FL dies better then Hornady, the expander is always centered in those, and the Hornady set up takes a lot of patience to get centered. Now, you have the option to set the expander high in the Hornady dies to mimic Forster (neck still mostly in the sizing section while being expanded on the downstroke) which is supposed to increase concentricity. It does require decapping separately if you do that. The Hornady neck size dies also do several different cartridges of the same caliber, they are basically a hollowed out FL die and require some fine tuning to size the neck of various cartridges, not just screw down to shell holder and size set up.
Hornady dies are finished better, and when I've had both sets for the same cartridge, I found Hornady FL size a little less then Lee's do.
The Lee collet neck size dies are quite good though as well. Same with the factory crimp if you need to crimp, everything else sucks in comparison for crimping lol.
My own preferences are all over the place though, but Hornady or Redding shell holders only.
For hunting applications, or semi-auto plinking, Lee is all I need.
For a bit more accuracy in bolt guns I upgrade the seater to Hornady ($25US from Brownells) and get a Redding neck die ($30-35US Brownells).
If I want to wring everything I can out of a bolt gun, Forster neck dies ($35US Brownells) and their bench rest seater ($50US Brownells).