^^Beaten
No, you can wear and benefit from a non-magical shield while you are wearing a magical arms slot item. You can also wear a magical shield and magical arms slot item at the same time but you only get the magical benefits of one of them. You always get the shield's AC bonus regardless.
The restriction on magic item slots has nothing to do with shields. You can heft a shield and an arms-slot magic item provided there's no physical limitation preventing you. It just so happens that magic shield items are arms-slot magic items, but non-magical shields are not arms-slot magic items, because they are not magical.
If it helps, think of the "slots" kind of like chakras. They're key spots on your anatomy where specific spiritual/magical forces can channel and flow, and be manipulated and harnessed for various effects. But only so much energy can flow through any one given slot, so cannot power more than one magical item.
-Dan'L
I disagree. Why do you say otherwise?By FAQ yes, by RAW you only get the benefit of one item worn on your arm, magical or no.
Shields also make any class that can use them much better off using them with a one handed weapon with little to no differentiation when using arm slot items and a shield.
Player's Handbook said:page 224
Magic Item Categories
These are called item slots, and they provide a practical limit to the number of magic items you can wear and use. You can benefit from only one magic item that you wear in your arms slot even if, practically speaking, you can wear bracers and carry a shield at the same time.