Say that a creature uses a magic wand to cast a spell (e.g. Entangle). If the user is hit, do they need to make a Con saving throw to maintain concentration on the spell?
Concentration is concentration it doesn't matter if you cast the spell from an item or if you cast the spell from a spell slot.
The spell uses its normal casting time, range, and duration, and the user of the item must concentrate if the spell requires concentration.
PHB p203 indicates the rules on when concentration can be broken which include: taking damage, casting another spell (regardless of source) that requires concentration and being killed or incapacitated.
All this said there is a notable exception. Certain sentient items can actually cast a spell themselves and maintain the concentration freeing the wielder from doing so. Blackrazor is an example of that.
For the specific item 'Wand of Entangle,' yes. In general, it depends, as wands are not described as either 'cast from the item,' like a scroll, or 'bypass the casting of a spell,' like a potion.
Some magic items allow the user to cast a spell from the item. The spell is cast at the lowest possible spell level, doesn't expend any of the user's spell slots, and requires no components, unless the item's description says otherwise. The spell uses its normal casting time, range, and duration, and the user of the item must concentrate if the spell requires concentration. Many items, such as potions, bypass the casting of a spell and confer the spell's effects, with their usual duration.
Most but not all wands include in their description "to cast." Those that do not would fall under the bypass catagory.