I have a Waeco CF-110 that is running continously for 8 months of the year and this is the second year so I think it is doing well. You want to set it right and keep it in the shade well ventilated. At 20c ambient and a setting of 4c it is probably running 20% of the time.
Its actually better for a fridge/freezer with compressor to run it rather than let it sit unplugged. As long as you keep a battery tender on the aux battery (assuming you are running it from the aux battery ) so the fridge doesn't drain it down...
No chance in ruining the fridge by having it run as spressomon mentioned. For the last two years I've run my CF-50 nearly all summer without issue and when not in the truck it's the garage fridge. So no worries, especially if you've got a 2nd battery.
Some people who are off the grid run 2-3 of these as their household fridge constantly from wind and solar power.
The Danfoss BD35 is probably the worlds top and most commonly used compressor