I had a +3 steel shield with 5 and 7 shield skill on different gens. It is basically a compromise between the steel covered round shield and the huscarl shield. Amazing coverage , very high durability, but a very slow. With high shield skill (7+) you can take many hits, even from a 2 handed axe. Hardly anyone uses it, but if you are going for a build with high shield skill try it out before dropping the idea. I know people in the duel server have tested it and you can catch HUNDREDS of arrows. That's multiple archers with 2 full slots firing at only you.
The speed rating is very low, and makes it tough to use well with only 6 shield skill. If you can block quickly enough though, it is hands down the strongest shield in the game. Battle server matches don't last long enough to really take full advantage of it. In strategus, no army ever has them. But on the siege server and DTV, the steel shield is godly. You will run out of patience or lose area control due to your team before the shield breaks. 100% of the time.
Also the model is very shiny and gives you a unique appearance in game!
I'd like to see it rebalanced since so few players use it, but if done correctly it is not weak at all.