I know they use a different kind of relay for the dimmer, but I'm not sure what the actual differences are. I'm wanting to replace a dimmer switch with one of these two, and not sure which to go with.
This is the only light on the switch. It has led lights.
I think you have a typo in the title? You listed the same model twice.
Difference between the Zooz Zen72 and Zen72?
I would say none, they are both exactly the same! Although I like the Zen 72 better than the Zen 72 for its lower price. 
They have a comparison of the ZEN2x models linked to here:
https://www.support.getzooz.com/kb/article/728-zen2x-vs-zen7x-models-what-s-the-difference/
The page they link to only mentions the 2x models, not the 7x models, but at the top of this page, they also have a comparison of which 7x models correspond to the 2x models, which I assume is intended to mean they should be similar aside from the 7x upgrades. So, if you're trying to decide from among the 7x offerings, the page should still help. 
(And if you're trying to decide from 2x vs 7x, I'd personally opt for the 7x at this point for the newer/700-series Z-Wave among other things, but either should technically work.)
Their support is also great, so if you still have questions after looking at all that, I wouldn't hesitate to ask.
Oops, lol. Fixed it. Meant Zen77 and Zen72.
The ZEN27/77 are easier to wire in a 3-way, support most (all?) LED bulbs. I have mostly ZEN27 and have not had any flickering issues. I even have some not recommended FIET bulbs that seem to be fine. The only advantage the ZEN22/72 has is it can support higher wattages. But with LED bulbs you would need a lot, or large bulbs to hit the limit (100W on the ZEN77 and a typical LED bulb is around 8W).
https://www.support.getzooz.com/kb/article/151-zen22-ver-20-vs-zen27-whats-the-difference/
I tried zen77 for some recessed LED bulbs (pretty standard ones), but the different relay type in the zen77 made it to where there was a small bit of voltage leakage - the bulbs would glow dimly even when the switch was off. I was advised to try zen72 instead, since the different relay type prevents that sort of voltage leak. The advantage of zen77, attributable to the different relay type, is it's easier to wire for 3-way and 4-way. However, one potential disadvantage I've found is that zen77 is more susceptible to voltage leaks. My takeaway from my experience is that I am using zen72 for single pole installs and trying zen77 for 3-way and 4-way installs.
I recently installed Zen72
Works fine as a switch, but I'm having a really hard time finding a bulb that would not buzz when I'm dimming it
Tried two different CREE bulbs and one GE and they all buzzed on a single pole install
Zooz support is very good and response fast, but they can't suggest what bulbs should I use
Download the Hubitat app
