How are you supplying air to your plants? Your high humidity may be a result of not enough air exchange in your grow space. Your plants need a continuous supply of fresh air. Certainly, you have to get RH well down from 80% during late flowering, or you are headed for trouble with bud rot.
As to the specific dehumidifier, I have my doubts about the one you are looking at. I can't find specific information on it, but it is most likely a thermoelectric Peltier unit with no compressor, and they are often reviewed poorly regarding actual amount of water collected. If your closet is already getting to 80% before flowering, I doubt that putting the unit you suggest in there will get your humidity low enough.
If I were you, I would think about getting a compressor dehumidifier for the hallway outside your closet and make sure that you have enough air exchange to prevent the humidity inside the closet from getting too high. This may, or may not, be feasible depending on your ambient RH, and whether the hallway can be kept sufficiently isolated from the rest of your home to give a dehumidifier a chance to do the job. Perhaps the portion of the hallway near the closet could be isolated better by hanging a curtain of polyethylene plastic or the like.
In any case, your closet needs ventilation, and one of those Peltier mini dehumidifiers seems unlikely to me to keep up with your plants.
Good luck with it.
