William Optics, Celestron, Telescope Service, Orion, Omegon, Astro-Professional, and simillar
All these binoviewers comes from same factory in China, from Kunming United Optics Corporation.
Here is link
You can also order your own binos with little different outside colours and design which they offer, with your own logo, but you must have company, and you must order minimum amount they require (not small amounts).
There is absolutely no difference optically (except difference sometimes in coating colour, all becasue difference in position of coated surface in time when optics are coated in relation vs source which coat).
All prisms and correcting glass, are 25mm in diameter, with same glass material, and same polished surface factor.
Clear aperture on each eyepeice side is 20-21mm, and on telescope side 23mm.
These binoviewers beleive or not, produce one of most brightest images of all binos in market.
Downsides are, not excellent mechanical construction as Zeiss, Baadere and simillar offer, and smaler prisms than bigger one units.
William Optics and units with same or simillar eyepeice holders, have shortest light path, while units like Omegon, TS and simillar, have longest light path, but with better eyepiece holders, which are self centring system.
Very good value for money!