Well, they are much more capable of reproducing the full range of forces at more accurate and realistic levels. The only real problem is that most FFB sims don't provide the proper ratio of forces to the wheel, because they are designed to work with much weaker wheels, so all the forces are condensed down to compensate. This is more easily gotten 'round with PC sims since they usually have a lot of adjustment range in the .ini. I noticed this a lot with my CSW mods; when I'm running at 40V, the wheel is capable of producing over 10N•m of torque, but it is waay too strong when playing GT5 or other console games when just steering, since the game has that effect "turned up" to compensate for weaker stock wheels.
Pretty sure with the ballscrew w/antibacklash Wheels, the benefit is immediacy and accuracy. Actually, what even the weakest of these "direct drive" (my description, not theirs) wheels cope with in terms of forces is quite impressive considering what they are effectively doing is making a wheel that does not magnify its ffb force by using belts, gears, or any other such engineering trick to put out more force than the motor is capable of.
Think of it this way, what Leo, Frex, and ECCI do with their wheels is compete performance wise with Logitec, TM, and Fanatec. If all of them were racecars, the latter group of belt driven wheels have the most (and least) advanced axels coming off of the motor and transmission and are tuned as such (to compensate for the ratio of the drive axel, linkage, and gears in the transmission. What the Antibacklash "direct drive" group of wheels do is effectively hook a motor up to each or both rear wheels and then have the driver opening and shutting carburetor jets manually.
I suppose the engineering tricks of the belt and gear driven wheels will have more brut performance which is nice but imprecise if all else was equal. But, if you could somehow match the brute performance of the belt driven wheels without the slop that amplification of inputs brings, you really would have something special.
Keep in mind I'm a big fan of Fanatec, and own a CSR elite currently, and am perfectly happy with it. In fact, I also have frex pedals that I can't figure out how to make USB stand alone because of the mind-numbing complication of the hydro-brake and simcaliper, and have been scouring the internet for hints on how to make it work without any luck. If Fanatec made the pedals I have, I'd have a new set already or instructions on how to make them work as well as timely correspondence about the problem I've made for myself. Instead, frex is ignoring me, and the only info on their website says I need the brain for their motion cockpit contraption or a frex wheel and controller box to make them work (though I can try their $80 usb board, if I feel like waiting for 6 weeks to receive it after giving some japanese dude I have never met all my financial info (which he already has btw)).
Fanatec has done nothing but bend over backward to make things right for me and many other customers and should be applauded for going the extra mile to please their customers. This attitude is exceedingly rare these days, especially in the consumer electronics industry. For instance, my first G25 had a faulty motor in it. This fact is indisputable, but the hoops I had to jump through to get a replacement involved countless hours of talking on the phone with CS agents, showing I had the original receipt for it, had registered it with matching info correctly before starting the RMA process, after going through 24 hours on the phone (collectively), 3 levels of support, and $50 shipping cost. Then I got to wait 4-6 weeks (2.5 months actually) to get a wheel. Not a wheel and pedals, just a wheel, which sucked because I think the CS agent told me to send "everything" to them, and when they receive it, they'll verify the flaw (sure they will), and after that they would send a new one. Well I had to wait another 4-6 weeks (3 months), for them to send the rest of the stuff I had just sent back to them. I got to pay for the privilege too.
... and what really chaps my a#% is they didn't even apologize.