I think "Dead Length Seating die" is just what Lee calls their seating die. Correct me if I'm wrong but I don't think there's a Lee standard seating die and a dead length,,
That said alot of guy's like the Lee's, I've only tried one set in 308 and traded it off for RCBS. It was the 3 pc set with Crimp, FL and Seater and it was the Seater I didn't like, just couldn't get used too that floaty thing inside there. The knob is nice instead of the RCBS nut and rod adjustment but I can make tiny adjustments with that set-up just fine.
I'm sure I'll try the Collet Die some day, But I'm content with my current RCBS seater