I have use both the Hollyland Solidcom C1 Pro and the Eartec Ultralite HD on several film projects and want to share my on set real world / use experience of both the products.
Hollyland Solidcom C1 Pro – https://amzn.to/465ydDm
Eartec UltraLite – https://amzn.to/3QUHRnR

Both are very similar intercom systems which allows multiple people to talk over the intercom, which is a very different system from Walkie Talkies where you can only talk one at the time. Also these systems work with a master / main headset which connects to all the remote headsets.

To activate the microphone , you just have to move it to the down position and you can start talking. This way you don’t have to hold down any buttons, but also allow you to talk while having both hands free to do your tasks.

Eventhough the EARTEC looks like an old established product due to the Y2K aesthetics design. But this UltraLITE HD was released in 2018. It might have been on purpose they designed it, to look old to make it looks like a product that has existed for many years. But the build quality of the UltraLite is quite low as its feels like made from cheap plastics and I have seen many more broken Eartec units, that are held together with gaffer tape to prevent the microphone to fall down.

Hollyland is overal a much more modern design and has a much better build quality. Also it is much better formfitting with its tops section and give less of a headache using it the whole day. Also you get a proper hardcase with the Hollyland to store it properly, while the Eartec goes into a flimsy bag.

Batterylife
Batterylife on the Hollyland is 10 hours for the Remote units, while the Master goes up to 5-6 hours, depending to how many Remote units it is connected to. A Tip is to swap the battery of the Master during any breaks, so you are sure the Master won’t run out of battery while working the whole day. But also luckily in the Solidcom packages its comes with additional extra batteries, so you don’t have to fear running out of batteries.
With the Eartec its a different story as all the units last up to 6 hours and you don’t get additional batteries with the set they sell. So you have to spend extra money buying an additional battery and also have to make sure mid day to swap out all the batteries.
Charging time
To fully recharge the Eartec batteries it takes about 3 hours and often after the wrap, we notice we have to let it recharge overnight. While with the Hollyland, we often start charging before we pack up and often when we have everything packed the Hollyland batteries will be al fully recharged.
Range
From my own experience we have a much better range with the Hollyland and often could stand 100 meters away with even few walls in between and still able to talk to each other. But also talk to each other from the chase car to the main car. And often able to the best boy in the Gaffer Van from inside the building. While with the Eartec had issue going pass 50 meters and also if there is more than 1 wall between the Main headset and the remote, the headsets would disconnect from each other.
Annoyance
One thing that is very annoying on the Eartec is the beeps. When the headsets disconnect from the Main headset, it will start beeping in a certain way. It actually gets quite annoying very fast and also very distracting. While the Hollyland will tell you what is wrong once and then keeps the signal silent.
Something I want to see
A feature I would like to see are seperate channels, especially on a filmset we have different departments who needs to communicate with each other from a distance. As it is quite distracting to hear questions from other departments and its just nicer to specify each department to have their own channel to communicate on and also less chance for certain confusions.

Conclusion
Both are competent intercom systems that are useable to on filmsets. If you need to rent them both will do its job. Depending how long the shooting days are, you might want to opt for the Hollyland which can last longer with the remote units. However if you plan on purchasing the headsets, I wouldn’t cheap out for the more affordable Eartec and just spend a bit more on the Hollyland Solidcom C1 Pro, which is just a much nicer system to work with.