You gain increased proficiency, damage and can use one entanglement per turn while using any whip. A character can dual wield a whip without the dual wield feat when not using a shield or two handed weapons.
Any whip action can be used with a 20' reach, the to hit roll is 1d20 + proficiency bonus + dex/str modifier, damage per attack is increased to 1d6 + proficiency bonus + dex/str modifier and you gain one bonus action per attack which is 1) bonus attack damage 1d4 + proficiency bonus + dex/str modifier or 2) extra opportunity attack or 3) one entanglement per turn.
Note, other character attacks, movement, spells and actions can be taken during a turn, but only one entanglement action with a whip per turn.
A whip reaction is always available 1) to hit is 1d20 + proficiency bonus + dex/str modifier 2) damage is 1d4 + proficiency bonus + dex/str modifier 3) extra opportunity attack or 4) only one entanglement per turn.
Entanglement is able to knock prone, trip, restrain, grapple, disarm, swing 20', stop falls and to automatically do normal tasks like pull objects to you, move objects, move levers, climb 20', push objects 5', etc.
Entanglement Attack/Save DC is DC 10 + proficiency bonus + dex/str modifier or automatic for normal tasks.
You can use the Whip Entanglement feat freely without ever losing concentration on any spells.
Examples of Whip Entanglement Feat During a Turn:
A) A spell could be concentrated on freely, a reaction attack to someone entering within 20', then two attacks with two bonus attacks also in a turn and then a final opportunity attack.
B) A spell could be concentrated on freely, then a reaction to someone entering within 20', then an opportunity attack with a whip all BEFORE one attack hits with damage and then only one whip entanglement action is used (DC Save is rolled successfully) restraining a monster on your turn! The rest of your turn could be moving 15' and two attacks with advantage could be used in your turn with a weapon in your other hand, then finally moving 15' away.
Comments