We had a fellow use one of these in a recent long range course we offer. I had not seen them work before, and for the most part, I'm not a fan of any style of hold-over reticle (including the Horus)... too much clutter in the lower half of the reticle really does negatively impact your ability to see ground strikes near the target, and that of course makes it impossible to make a hold correction on a follow up shot. Keyboard commandos never need a second shot of course, but if you're really out there shooting it's gonna happen... :/
The Shepherd isn't too "busy" however... and it did a decent job for the student. What you have to know (which is the case with any hold-over reticle) is that as your altitude and temperature changes (DA), the hold over points after you pass about 600 yards will not be "spot on", and you need to know how to compensate for that. Good notes will help...
Windage holds could be an issue as shovel mentioned above... his points are worth noting.
The Shepherd scopes can be made to work. Not a first or second or third choice, but they'll work. I don't know if I'd want to have more than 300 dollars or so invested in one (just because there are better options out there for that price point, such as Weaver Grand Slam and SWFA 12x)... but after you learn to zero the thing (which we had to look up online, as even the scope's owner didn't know how to do it), it'll work. We took the shooter, who used a 308 and typical 175 grain match load, all the way to our 1040 yard plate with respectable hit counts.
Dan