Hi, I think as the live view is from the sensor live view should be good, dont forget to use 10x zoom. I have had some OOF live view AF issues but as you will be focusing manually this will not be an issue. If you are wanting easier focusing and you have an android tablet you could do worse than the USB adaptor lead and DSLR Controller software, this gives you a much larger screen and control of all shooting controls and you can zoom x10 that too!
I have tried the reverser rings, they work really well but dof is sooo thin you really need a lens with a good long focus action to enable accurate focusing.
I'm sure you will have fun whichever you use.
7DII+Grip, 7D+Grip, 40D+Grip, 5D+Grip, EF 24-105 f4L EF-S 17-85, EF-S 10-22, EF 70-200 f2.8 L IS II, EF 2x III, Σ150-500, Σ17-70 f2.8-4 C, EF 50mm f1.8, 550EX, Triopo TR-985, Godox FC-16, Filters Remotes Macro tubes Tripod heads etc!
5D, 20D, 24-105, BG-E4, BG-E2N, 17-85, Nifty 50 pre owned. 😀