Good question.
If its with regard to the T-7 vs other turrets, the T-7 has simply out shined its competition at providing functionality and quality vs price.
If its with regard to the T-7 turret vs a different system, it gets more complicated.
In its simplest form a single stage (SS) press permits the use of each die in sequence and requires that you set up and adjust a die each and every time you use it. You economize your time by performing each reloading step in batches to cut down on time required to set up dies. This is economical and functionally optimum for small batches (50) and high precision. Benchrest rifle shooters typically stick with these.
At the other end of the spectrum, both in function and price, you have progressive presses. Upon these you mount multiple dies on a multi-place tool head to which a multi-place rotating shell holder presents a corresponding number of casings each time you pull the handle. Its a mini assembly line, if you will, accepting a raw fired casing and producing a completed reloaded cartridge with each pull of the handle. Bench rest rifle shooters don't use these, IPSC pistol and 3-gun shooters use nothing else. Set up and running, these will cough up 500 to 700 completed cartridges, of an acceptable quality, per hour. Progressives must be converted in order to produce various caliber cartridges. Conversion involves time and expense.
In the middle of the spectrum, you have Turrets, the Co-Ax, SS presses that accept bayonet die mounts like Hornady's L&L system, multi place presses, etc. These are essentially SS presses that employ a system that wholly or partially eliminate the tedious need for resetting dies all the time. Faster, but less precise (except for the Co-Ax), than a basic SS but slower, and more precise, than a progressive these systems generally fill the void between the two. If this isn't complicated enough, there are Reloaders out there who set up a Dillon 550 (non auto-indexing) for each pistol caliber they shoot, thus avoiding setups and conversions altogether.
This comparison is rough and leaves out quite a bit of detail haha, but should nonetheless give you a general idea. What you should start with is a single stage like the Co-Ax or else one that accepts Hornady's L&L bushing system, (not all do). As your reloading style evolves you may eventually get an auto-progressive or a bank of 550's, but you'll also keep and use your SS press. A basic SS press remains a useful tool on every reloading bench regardless of whatever else is bolted to it.
Now, get on line and order yourself a catalog from "Sinclair International" and drive yourself nuts
.
