1) Sliding trays (plastic) vs fixed trays (metal).
I prefer the sliding trays to facilitate the accessability of my items, without reaching deep within to get or place them back.
2) Power cable is perm fixed vs those removable cables that's commonly used for computers
Makes no difference as it's plugged in and always on.
3) Colored RH knob & no lights vs non colored RH knob with 2 light indicators.
I rather have the 2 light indicators to know that the dehumidifying unit is working! 
Can someone tell me which is older/better. And if there's anything in particular to look out for when purchasing?
But a bigger one that required to give room when the number of your gear expands! 