Steve,
I tried some indoor test shots using the screen to focus and seemed to hit the spot okay using a bar code for the target at the 180L's MFD. I suspect that a fly's compound eye would be a little more challenging though.
I also have the 10 metre extension for remote shooting but this would entail automatic focussing and that's probably not ideal for high magnification shots.
Generally, it's a useful bit of kit. It may not quite match the liveview bodies for quality but has lots of advantages that make it a unique product.
Bob