I own a Razor UHD 18x56 (got an exceptional deal and couldn’t resist) and have done some playing around with both the 15x and 18x B5.
Both the UHD and B5 are fairly well constructed. However, the focus wheel on the UHD is glued on and the part of mine (the end cap) has come off. It doesn’t effect any performance but it makes an otherwise premium binocular feel cheap - although the housing is rock solid. So, I’d have to give a slight nod in overall build quality and refinement to the Mavens. Both have no-question warranties.
UHD and B5 optics are of similar quality and either will get the job done for long-range spotting. However, IMO 18x is just a bit too much and begins to make minor flaws in the view a bit more noticeable. I also see a slight bit more CA in the UHD. But overall see the UHD and B5 are about equal. Both use high-end glass and Abbe-Koenig Prisms in their optical design. Interestingly, the B5 uses higher fluorite content glass in the B5 as compare to the rest of the Maven line. To me, the better choice is the B5 in 15x56. The image is brighter, slightly crisper, with fewer visible aberrations. IME, optical designs have their peak performance at specific magnifications. IMO, the B5 15x56 is the cherry. Do I like it better than the UHD? = a smidge. However, the difference hasn’t been enough to get me to toss my UHD and buy a B5.
Just to get out in front of a frequent follow up when discussing these particular binoculars. The SLC 15x56 is a slightly better performer than either the B5 or UHD, Whether it is worth the extra $ is a personal choice.