I've never seen a gel humidifier that actually offers 2 way control but there's always a first I guess. I've no idea what fluid or salt they're using in the gel so it's possible I guess but I would doubt its effectiveness.

I have a few gel tubes in a couple humidors (not xikar ones) but I have at least 1 boveda in each as well to suck up extra humidity. Seems to be a good combo too. The gel humidifiers keep the boveda from drying out too quickly.