Is theft/security an issue for you? Mature Christmas trees must be one of the highest-value crops you can steal from a farm, and one of the easiest to fence.
There are pros and cons to the different business models, but in this case, if you think of it as a matching/sorting type of problem, it's inefficient and wasteful, in a logistical/Nash equilibrium sort of way.
Which doesn't always mean it's the wrong way, from a business perspective. But if you're charging by height, it's leaving money on the table.
It's not an issue on our farm. We have eyes on most of the property most of the time. We also don't stock any precuts, so a thief has to come on the property and do some amount of work to steal a single tree.
>Mature Christmas trees must be one of the highest-value crops you can steal from a farm
If you have the equipment/motivation to steal christmas trees, you probably could be stealing animals too. Those are proabbly worth even more than christmas trees, probably several hundred dollars each.
Harder to dispose of, though. You'll need to be in league with a crooked farmer, slaughterhouse or livestock mart if you want to sell the animal alive. You can sell Christmas trees on the side of the road, no questions asked.
People with 7-8' ceilings cut the top 6' out of a 12' tree bc they didn't like any of the younger trees.