I bet studs bit into the ice more then flat screw ends, but I have never used screw shoes. What you prefer to use is up to personal preferences. I have used my orienteering shoes now for 4 years and no signs of wearing. Not bad.
About wearing out the shoes. I weight only 65kg, I have run whole my life. My summer shoes last for 22 months. I run apprx.25-35 miles per week. So maybe I do not wear shoes out so much.
But as overall orienteering shoes do not wear as quickly as normal running shoes. Mostly because they are made to last heavy wear during the forest runs. I dare to say that even for heavier runner orienteering shoes last many years if done only winter running in roads and trails.
That way the cost is not that bad for a year.
The roads I run on are dry 90% of the route, but there is the occasional melted snow that drips/runs out a couple feet into the road and re-freezes. It's usually thin and smooth and tough to spot.
I would seem overkill to use screw shoes or similar type devices. The reality is I have to see it to avoid it and as a result it's kept me from night running.
Slip-ons / strap-on devices are heavy, uncomfortable and not runner friendly.
Screw shoes work on mixed surface very well -- we have A LOT of black ice around here. I had used those for several seasons with the only drawback being how quickly they wear out (about 1 week).
I found a great solution last year called Icespike ( http://icespike.net ) -- mine lasted the whole winter (in NH that is 4+ months!). I also saw them at an EMS store last weekend, if you would rather see in person. This is the first product that I have found that keeps me outside in the winter rather than on my treadmill!!
Slowing down and a head lamp are the tricks that have worked best for me so far. Balance helps but isn't everything... some spots are just plain tricky to run on. I have tried YakTrax but found them not to be effective in spots. I saw a product this year that I am going to try- Stabilicers... looks to be a winner... but I am not sure yet.
We run weekly hill sessions at night with headlamps. We pick a long and quiet road. First pass up you access the road conditions and adjust accordingly (pretty rare for us to need the Yaktracks on these runs in NH).
Great alternative to tempo runs, and depending on the hill, 10 repeats make for a very good workout. We warm up ahead of time running easy on the roads, same after.