From what I’ve seen the cheap hobby driers look like they suck. I think there is supposed to be some kind of hazard with silica desiccant, and maybe with the color change type specifically, I honestly don’t recall the details. However, if you use the color change type spread out in a drier/container in different areas, and you leave the filament in there for several days with the heater running you’ll see how moisture is distributed.

I’ve seen tear down videos of several filament drier units, and have never been impressed by any of them. They are made to look a certain way, but the designs suck. I built a drier with a small convection oven and a PID controller. This has a circulation fan and heating element that is more than capable of maintaining any temp I want. The problem is the size of the dumb thing. Most of the time I end up using a plastic cereal container with a layer of color change desiccant, the filament, and an old food hotplate warmer placed in the container. The hotplate is not adjustable. It has a 60C thermal switch. I’ve left filament in this setup for several days just to see what happened. You could see the convection current pattern in the color change. Even with the filament standing up, and the hotplate upright beside it, the moisture color pattern didn’t completely cover the filament on the spool. I use one of the ancient 1970’s hotplates with a rectangular glass element surface and frame. Inside it is just mica and nichrome wire, but it is a much larger element than any of the cheap filament driers at 100 Watts and it stands at around 2/3rds the size of a typical 1kg spool. If this barely not quite works to create an effective dry area larger than a spool in a sealed container, the commercial drier units are very sketchy. I think this is why most people end up using other stuff and why I’ve avoided them. The biggest problem IMO is a drier that works well while printing and doesn’t take up a lot of space.