Can Tortles receive the non-AC benefits from magic armor?

The Tortle’s Natural Armor trait says:

Due to your shell and the shape of your body, you are ill-suited to wearing armor. Your shell provides ample protection, however; it gives you a base AC of 17 (your Dexterity modifier doesn’t affect this number). You gain no benefit from wearing armor, but if you are using a shield, you can apply the shield’s bonus as normal.

My question is whether or not this means all benefits from armor are ignored, or if it’s just the AC benefits. For example, if a Tortle is wearing adamantine armor, its AC is still 17, but is it still able to be critically hit? Same goes for items like Hide of the Feral Guardian or Mizzium Armor; would you be able to use an action from the armor to cast polymorph on yourself/would you take no damage on successful Strength and Constitution saving throws?

How does a Cloak of Displacement interact with a tortle’s Shell Defense?

The cloak has a property that causes creatures to have disadvantage on attack rolls against the one wearing it, and

This property is suppressed while you are incapacitated, restrained, or otherwise unable to move (DMG, pg 158).

The way Shell Defense is described

You can withdraw into your shell as an action… While in your shell, you are prone, your speed is 0 and can’t increase, you have disadvantage on Dexterity saving throws, you can’t take reactions, and the only action you can take is a bonus action to emerge from your shell (EGW, pg 181).

is effectively the same as being both incapacitated and restrained, with the only notable difference being that an attack against a prone creature

has advantage if the attacker is within 5 feet of the creature. Otherwise, the attack roll has disadvantage (PHB, pg 292).

While extremely similar mechanically, the tortle using Shell Defense is technically neither restrained nor incapacitated. Furthermore, the ability to emerge from its shell as a bonus action implies the capacity to then move during that turn if the tortle chooses to, so neither are they otherwise unable to move.

As such, would the Cloak of Displacement work for a tortle using Shell Defense (and thus cancel out the advantage melee attackers would normally have due to the prone condition)?

RAW and RAI interpretations are both desired.

Does a Tortle’s Natural Armor interfere with the Monk’s Unarmored Movement ability?

The Tortle’s Natural Armor ability says:

Due to your shell and the shape of your body, you are ill-suited to wearing armor. Your shell provides ample protection, however; it gives you a base AC of 17 (your Dexterity modifier doesn’t affect this number). You gain no benefit from wearing armor, but if you are using a shield, you can apply the shield’s bonus as normal.

The Monk’s Unarmored Movement ability says:

Starting at 2nd level, your speed increases by 10 feet while you are not wearing armor or wielding a shield. This bonus increases when you reach certain monk levels, as shown in the Monk table.

The comments on this answer to a related question briefly mention the interaction between Natural Armor and Unarmored Movement, but nothing conclusive is discussed.

It is not clear if Natural Armor counts as worn, or even as armor, for the purposes of the Monk’s Unarmored Movement Ability.

Does a Tortle’s Natural Armor interfere with the Monk’s Unarmored Movement ability?