I've been in both environments with different DTG printers. A former company used Brother's, and used a heat press for the pretreat step and also to cure the ink. They used a heat press when they just had the 541, but when they upgraded to the 782 this became an issue curing the ink as the model heat press they had caused numerous issues. Before they purchased the new printer, I recommended using a heat tunnel, but the owners decided they didn't want to spend the money. This decision ended up being a detrimental one as they found that a heat press wasn't applicable to all garments, caused issues with workflow and wash-ability afterwards.
The company I work for now uses two Kornits, and we use a heat tunnel to cure the ink. Works beautifully, and having the pretreatment as a built in step is much, much better for the workflow.
There are plenty of used dryers on the market, and if you can afford one I would recommend using a heat tunnel to cure the ink. I'm sure there will be plenty of people that suggest that using a heat press is sufficient, but in my experience using a tunnel provides easier labor and more consistent curing of the shirts.