Hello there!
1. It should have gained EVs for sure if its EVs are less than 510 in total, meaning from all the stats sum should not be more than 510 for the pokemon not to gain EVs there after.
2. Yes, the pokemon's speed statis reduced to half, meaning both in-battle and out of battle, if the pokemon holds the item, its speed is reduced to half. however, outside of battle, the effects are unknown.
Let me know if you have further questions.
Deep Regards.
- Aghanim.