Is it safe to open Reckon one in multiple windows and enter data without causing data corruption?
I think it is safe to do so. As long as you are opening them in different browsers. Or if you are using 1 browser (ie chrome), one can be in normal mode, another in incognito mode.
Sorry, didn't read your question clear enough. If you work with one file, you can open as many windows as you want without causing any corruption.
Phuong Do / Reckon Developer Partner