I fiddled with one once and found it to be a poor compromise between bino's and a spotter.While intriguing, aside from the weight and pack volume savings you might be dissatisfied with the end result in the field. There's a reason you don't see professional guides or highly successful backcountry hunters rolling with bino's and a doubler. It's always bino's and a spotter that are suitable for the country and animals being pursued.
That said, I see people with high quality "big three" bino's that tote along a bargain basement spotter that might as well be a heavy cardboard tube with stained glass for lenses. Meaning if you start with a high quality pair of bino's and throw a doubler on it, you'll likely get better optical clarity at a fraction of the price and weight of a low grade spotter. So, you might like it...Check out the return policy and try one.

Personally, I think the best setup is 10x bino's (or preferably 15x in bigger country) on a tripod, with a big spotter for zooming in on details. Back that spotter up with a PhoneSkope adapter for even more zoom and you'll save yourself a whole lot of walking.
Regards,
Allen