Do Dimensional Shackles share any of the properties of Manacles?

Question

The Dimensional Shackles state:

You can use an action to place these shackles on an incapacitated creature. The shackles adjust to fit a creature of Small to Large size. In addition to serving as mundane manacles, the shackles prevent a creature bound by them from using any method of extradimensional movement, including teleportation or travel to a different plane of existence. They don't prevent the creature from passing through an interdimensional portal.

You and any creature you designate when you use the shackles can use an action to remove them. Once every 30 days, the bound creature can make a DC 30 Strength (Athletics) check. On a success, the creature breaks free and destroys the shackles.

Does the bolded text mean that they actually have all the properties of regular Manacles?:

These metal restraints can bind a Small or Medium creature. Escaping the manacles requires a successful DC 20 Dexterity check. Breaking them requires a successful DC 20 Strength check. Each set of manacles comes with one key. Without the key, a creature proficient with thieves' tools can pick the manacles' lock with a successful DC 15 Dexterity check. Manacles have 15 hit points.

In particular then:

• Can Dimensional Shackles be escaped with a DC 20 Dexterity Check?
• Can you break them with a DC 20 Strength check?
• Can somebody else break them with a DC 20 Strength check? (The DC 30 check only applies to the bound creature, unlike with Manacles, where any creature may attempt to break them)
• Do they come with a key?
• Can they be opened with a DC 15 Dexterity Check using Thieves' Tools?
• Do they have 15 hit points?

For example, if they only have 15 hit points, couldn't you simply headbutt them until they broke, which would take far less than 30 days.

Answer 1

2:

Can you break them with a DC 20 Strength check??

No, this directly says otherwise:

Once every 30 days, the bound creature can make a DC 30 Strength (Athletics) check. On a success, the creature breaks free and destroys the shackles.

4:

Can Dimensional Shackles be escaped with a DC 20 Dexterity Check?

You can use an action to place these shackles on an incapacitated creature... You and any creature you designate when you use the shackles can use an action to remove them.

I think because of this condition nobody thought a key would be needed for the shackles, so normally the shackles wouldn't come with a key. That said, having a key for the manacles would indeed be incredibly useful, if not, scary to not have. You're bringing around shackles that won't come off so simply if an enemy took them and slapped them on your wrists while you slept or were distracted at a bar? And these shackles don't have a key?! No thank you! I would have nightmares of people slighting these cuffs off of me only to throw them on me as a prank. I think anybody using these would want a hidden key to keep in their boot. As a DM I might give a key. Not necessarily though.

Regarding points 1, 3, and 5: without a specific rule I would have to say no to all of them, there is no specific rule that would allow either. Since it isn't specified it would be a house-rule to allow any of these rules to work. In regards to another person being able to make a strength check to break them, I would rule that this can be attempted, but they have to roll 30, not 20.

6: This would be ridiculous. It seems the shackles were meant to be difficult to get off. You need to make a strength save of 30 to break them, but they could be destroyed by one powerful spell? or 15 turns of unarmed attack. The item seems tailor made to prevent mages from teleporting, but they can blast it with a single disintegrate and teleport away anyway, while you lost a rare item. These shackles wouldn't be worth their while if they were so easy to break. They would be better used on a big, tough guy than someone with teleportation. Maybe they would still be useful as a precaution against misty step or dimension door. 15 HP would highly undermine the key feature of the dimensional shackles.

Honestly writing all this up gave perspective to the difference between 'serving as mundane manacles' and having 'the same properties as mundane manacles.' dimensional shackles should not have the same properties as mundane manacles, but do serve the same purpose: to bind someone. Having an additional purpose: to prevent the bound someone from teleporting away.