Do you understand how the different hubs work? Im asking because i did not before i asked the same question, then realised that these are much more practical. Heres a basic explaination....
Ok, so manual hubs you engage by turning the hubs on the outside to "lock". Then once they are locked, you can take the truck in and out of 4x4 any time you wanted. You can drive it in 2wd even with the hubs locked, without having to worry about wrecking anything. With the hubs locked, the front end is spinning with the tires, but not being pulled by the transfercase as its not engaged. So it still is slightly more work to turn... But it is not much difference as to unlocked at all. You already know the difference in mileage between being in 4x4 and not tho lol. So basically, you can (and i do) keep the hubs "locked" all winter and just switch it to 4x4 when you feel the need.
With auto hubs however, you must drive a certain distance before they actually engaged. So if you are driving along in 2wd and happen to get stuck, you cannot put it in 4x4 to get out as you cannot lock the hubs yourself.
So you and your buddy are driving around. You, with your manual locking hubs, and him with his auto locking hubs. Lets say he has this huge, beefy, lifted F250, and you have your current "little" ranger. But OH NO!... You guys end up getting stuck, both in 2wd because you didnt know you were going to need it. He is just spinning away and cannot get going, as his hubs arent locked in yet. You just simply walk out and lock in your hubs (providing you didnt lock them in the first place), and get in and put it in 4x4. You gett unstuck and pull out the truck twice your size that got stuck in the same place.
Moral of the story... Manual hubs are sooo much better and practical. Instead of having to drive 20 or so feet (or whatever it is... i never could remember lol). And if you just keep the hubs locked all winter, or even just when you think the roads might be bad out, you can go in and out of 4x4 whenever you want. It wont wreck anything.
Hope this helps you understand a bit about how it works.

I dont know the real specifics on it, but im sure if theres anything i missed someone else will clearify it.

People pay good money to switch to your current setup