It is highly recommended to download the server JAR and client launcher through official portals like Minecraft.net to ensure security.
Check out this detailed video review for a deeper dive into the specific changes and map compatibility in 1.8.1:
Significant improvements to the chunk rendering engine and game physics to reduce "lag spikes".
This version addressed several exploits that allowed players to crash servers. Major Features & Changes
Enhanced UI and stability for players using official Minecraft Realms.