I'll be honest, I've not used it as much as I'd have like to yet, but the lens feels well built and produces clear images, I've not done any rail & image stacking work yet, but the single shots on small bugs are good but tricky when they are running around, at f2.8 - f9 I can get away with OVF but f16 requires liveview as it's just too dark for OVF, some bright modelling lights are next on the list...

I seem to reach for 100mm x2 lens first, really need to stop buggering about around the hares and start macro again
The optional light for the front of the lens is pants, not bright enough for viewing at f16 hand held, I guess rail mounted it'll be fine for focusing at 2.8 and changing the dial after.
Sorry not much help