Binoviewers are one of those objects that divide the Astronomical community, some love them and some loathe them. My personal feeling is that when done right the binoviewer can be a magnificent piece of equipment but if the wrong pair are bought they can prove fiddly and frustrating.
Essentially, as its name suggests, the binoviewer is a sort of adaptor that fits into the eyepiece barrel of your telescope, in essence it's a pair of binoculars that plugs into your scope.
The pluses of a good binoviewer include a wonderful 3d effect on the objects you observe (especially on the planets), also I have been able to pull out finer details as it would seem the brain prefers viewing with two eyes rather than just the one.
It has to be said though that the Antares are not the best examples of a low cost binoviewer out there. My major grievances lie in the level of dimming that is exhibited in Antares' offering. Dimming is always going to be present in a budget binoviewer, unfortunately it's the nature of the beast. The more glass you put between you and what you're trying to observe the fainter the image will become (except when using very high quality, expensive lenses). Even expecting this I was surprised by just how dim these viewers are, especially at high magnification.
My second gripe comes from the mechanical operation of trying to achieve focus in both barrels for any length of time. As I have the older model, my eyepieces are secured into the binoviewer with one flimsy metal peg per barrel. This means that once I have brought both barrels to focus it's only a matter of minutes before the eyepieces have jiggled loose and I'm back to unfocused square one again. It's impossible to keep both eyepieces focused for a significant length of time.
I have heard that Antares have recently released a model that use a more secure method to hold the eyepieces in place, if I were buying these binoviewers again (and in truth I probably wouldn't bother) but if I was I'd get the newer model, from what I can tell the eyepiece screws directly into the barrel and there are no metal pegs in sight.
The 2 x 12mm and 2 x 15mm plossl eyepieces included in the set are good but could be bought separately, they would set you back only about £20 each. They are standard gso type plossls that are good for their extremely low price. It's just a shame they come with this lack lustre viewer.
If the Antares were the first pair of binos I'd ever looked through I would probably be put off for life, thankfully there are better viewers out there even in the budget category. If you choose to buy them the Antares bino and eyepiece set costs £150. You would be better off using the £150 on just the binoviewer and then add your eyepieces on to that.
In conclusion, the Antares is too dim and constant fiddling with focus will soon begin to grate on even the most patient observer. 2 stars instead of 1, because the eyepieces are surprisingly good for their low cost.