I tried it out in a one-shot last night and it worked really well! Even though I have a ton of premade, beautiful battlemaps on Roll20, I just loosely drew some maps, and when it came time to fight I added zones and tags. Here's an example:
(Ignore the blue squiggles at the top and the orange squares below, those were other maps.)
The characters were taking a shortcut through a dry gulch when they encountered two enemies (an elf captain and a gnome screamer) cutting a swatch through the forest on the other side of a grove of trees.
The characters wound up moving through the zones a lot, being chased by the Screamer (whose slow speed made him unable to dash through two zones), and firing spells from afar at the Lieutenant who had taken cover in the thick grove of trees.
At one point, the druid had climbed up a tree on the Steep Slope and was concentrating on Heat Metal on the Screamer (in this game, the Screamer was a gnome wearing a mech suit). The Screamer wound up launching rocks from the gulch at the tree, knocking the Druid down to the ground. Very cinematic and fun!
You can also see Spike Growth listed as a tag in the Grove, as the druid had cast it there at the end of the combat.
Some quick little rules we came up with on the fly:
1) Each Zone is "about" 30 feet across, unless otherwise stated.
2) Creatures cannot be adjacent if they are in two different zones.
In the future I might add something like "half cover" or "3/4 cover" or "lightly obscured" to zones, to remind me to use those rules for enemies. I forgot in the first round to give the Lieutenant cover in the trees, even though it made sense narratively.
Overall, a big success!