Hi,
I have one and I just love it! I rented it the first time a few years ago (just to make sure it would work before I purchased it) and even while just learning to use it the results for our farm were 100% accurate. I use mine regularly now. It may take some practice but once you get the hang of it you are spot on and can read a pregnancy in just a few seconds. I just checked some mares that are due in April and was still able to detect the pregnancy even with the baby down low.
It does work on other small animals as well, while I was at a friends checking her mares she asked if I would check her goat too. Well the pregscan said "YES" the goat was pregnant. Lo and behold just a few weeks later the cutest little kid popped out!
I really like that it is non-invasive. I have some very tiny little mares (under 28") that are really happy about it too.
If you have any questions just let me know. I am certainly happy to help. Oh yes, Animark is very good to work with. Phil Regas is wonderful and goes out of his way to help you with your purchase.
All in all, I wouldn't trade it for anything!!! It has saved me a substantional amount of money on vet bills too!