Since the mod is nearly a 1:1 copy, i'd advice you to Go read the Combat Tests wiki to know what it does.

Differences:

Improved attack indicator: Now the loading daggers also show the + simbol below when the crosshair is looking at an entity. Same way as the ready dagger does.
Since attacking with a shield is possible now. The loading daggers with the + simbol show below the shield icon.
Now i frames are Per-Source, meaning that multiple players can deal damage at the same time to the same entity, or a player and an entity can damage an entity at the same time. By default players are excluded from the Per-Source system, but i made a few improvements in case you want to be included: Player's armor and shield have a 1 second delay to receive damage again. Hurt animations must wait for the previous hurt animation to finish.
I frames adapt to the weapon's attack speed.
The player cannot interact with entities that are dying which allows them to attack thru them. If the entities death time is greater than 20 ticks (1 second) he'll be able to interact with them again, to ensure compatility with lootable corpses, such as ice and fire dragons.

Bonus:

The shield's strength and knockback resistance attributes scale with the shield's durability: starting from 400, shield's get 1 point of shield strength and 5% knockback resistance per 100 durability points. This can be adjusted manually in the config file.
The crossbow automatically seats the arrow.
The sprint toggle won't reset after death.

Stat conversion system: The mod automatically converts modded weapons stats to match better the damage nerfs and attack speed buffs done in the Combat Tests. If you want to check what the original stats of the item were, you can enable the SHOW ORIGINAL STATS TOOLTIP in the config file, and press shift while hovering over an item.

You can also adjust a weapon's stats manually in the config file, if you don't like how the mod converted them:

customWeaponStats = ["alexscaves:desolate_dagger;damage=6;speed=5;piercing=0.5;reach=4"]

customShieldStats = ["minecraft:shield;block_cap=5.0;kb_resistance=0.5"]

There's also a new armor piercing attribute, which is only accesible if you grant it to an item in the config file, currently.

Haven't added:
The health and hunger system.

Combat Improved