How do fly fishing rod reel seats vary and why?

Reel seats are interesting devices. They range in price from perhaps $10 to $60 or even more. One might question why it would make sense to put that much money into a reel seat if an inexpensive one would do the job. Let’s take a look.
The reel seat is the device that holds the reel on to the rod. Selection of a reel seat has more to do with aesthetics than anything else, with a couple of exceptions. A decent reel seat will hold the reel in place as well as a top of the line reel seat.

 Reel seats come with aluminum, titanium, graphite or wood arbors (the shaft section of the reel seat). Wood arbor reel seats are mainly used in freshwater fishing as the wood (unless varnished and cared for) does not stand up well to saltwater. Aluminum reel seats need to be anodized to avoid pitting and corrosion. Titanium reel seats have the lightness of aluminum with added hardness and resistance to scratches and dings.
Wood arbor reel seats use metal hardware (called a skeleton) to secure the reel in place. Less expensive reel seats use anodized aluminum skeletons. The best reel seats use jeweler’s grade nickel silver skeletons.

Reel seats come in uplocking and downlocking models. The difference is that uplocking reel seats lock the reel in tight against the grip while downlocking reel seats lock the reel tight against the butt. The significance of this is that the weight of the reel is shifted about an inch toward or away from the center of the rod, shifting the center of balance. The objective is to locate the center of balance of the rod directly underneath the hand when on the grip. This provides the least amount of fatigue. Most uplocking reel seats are recessed into the grip moving them even further up the rod.
A lighter reel is most likely best served with a downlocking reel seat, while a heaver reel is most likely best served by a uplocking reel seat. In fact, cigar grips are typically to narrow to accept the recess required by most uplocking reel seats.
Reels are held in place by a pair of ‘hoods’ that slide over the reel feet. One hood is fixed, while the other hood travels (uplocking/downlocking). The traveling hood is held over the reel foot with a knurled, threaded ring that screws the hood up tight. Better reel seats have machined threads that have a fine pitch (number of threads per inch) while less expensive reel seats are stamped and have a coarser pitch.
The threaded ring is kept from unscrewing by its friction against the traveling hood. Better reel seats keep the ring from working loose by having a secondary ring behind the first ring that can be tightened up against the first ring acting like a lock nut. Some have a rubber O-ring between the two rings that adds additional friction keeping the assembly from slipping altogether. The best reel seats do not require a second locking ring because they use a very fine thread pitch to keep the ring from working loose.

Finally, reel seats come with either a blunt butt and end-cap or with a fighting butt. A fighting butt is an additional appendage on the bottom of the reel seat that provides a cork (typically) knobbed foot that assists the angler in fighting the fish. Fighting butts are found only on heavier weight rods and make a lot of sense for rods 8 weight and above.