>Has anyone worked with OPOS or OlePOS driver for receipt printers?

Yes. Specifically for Epson receipt printers and cash drawers. Even with the same vendor, different models of printers have different printing formats, paper widths, etc. So unless you want to develop code for multiple models, define a specific model to be used [I support the Epson TM88-II only] and develop your printer code for that model. You don't have to concern yourself with cash drawer models. They all work the same and the code to pop them open works for any drawer. Just make sure you get the cash drawer from the same vendor. Epson's drawer connects directly to their receipt printers.

What I developed works extremely well with my VFP apps.