Sunstone Bracers doesn’t see much play because like most artifacts, it’s easy to remove. It also tends to have a small impact outside of the early game when having 3 Attack instead of 2 is huge. And honestly, if I want 1 more damage, I’ll play Bloodtear Alchemist. It has more reach, leaves a body, and is only 1 mana more expensive.
If there is a Lyonar deck running this card, they better have draw, because with a zero-cost card in-hand, they’ll probably empty their hand pretty quickly. I guess it can be useful if you need to use all of your mana to play a big minion, which allows your general to maybe take care of a 2-drop, but that’s really pushing its effectiveness.
I think this card is best against opposing Lyonar since the faction relies on minions sticking to the board. Being able to clear 2-drops efficiently early on might prove useful. (Why is Lyonar so weak to its own cards?)