OK, for all of you who believe that the latch is a security device to prevent
someone from entering your room, I have some shocking news... IT'S NOT!
A child can use a piece of paper to open from the outside in about 10 seconds. A practiced thief, 2 seconds. Hotel staff have a tool that allows them to open it from the outside.
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The purpose of the latch is to allow you to open the door partially and have a conversation safely or pass small objects through.
OP specifically asked about using a device because of WDW's new security check policy - in other words, to, literally, bar CM's from entering their room. If OP's intent is to DELAY entry with the bar, there is no need to bring one as the latch serves that purpose. If OP is looking to bar entry altogether, I would wager a BIG bet, that will not end well for OP. WDW staff has every right to enter the hotel rooms and WDW specifically states that right in their booking terms and conditions.
Yes, the latch WILL temporarily bar someone from entering your room. It gives you a chance to compose yourself, get to the door and allow the CM to enter. If you do not allow entry, of course, the CM's have every right to open the latch.
If OP's goal is to completely prevent CM's from entering the room, it is not going to go well. As you note, the purpose of the latch is to allow the guest to "open the door partially and have a conversation safely". You then either need to let the CM in or, if the CM goes away temporarily, allow them entry at another time soon after.
These are the current terms and conditions of a WDW resort stay:
Please be advised that notwithstanding your use of a sign on your door, a request by you to forego housekeeping services or
any other request made by you, the hotel and its staff
reserve the right to enter your room for any purposes including, but not limited to, performing maintenance and repairs or checking on the
safety and security of guests and
property. The hotel staff will give reasonable notice prior to entry
by knocking and announcing the intent to enter the room.
Again, the latch will do the trick to give you time to delay entry of the CM. That is all that any of us are within our rights to do.