Any magnification increase observed from increasing the distance of the eyepiece from the standard ep position in the barlow? That's a characteristic of a Barlow and not a TeleXtender/powermate type design.
Thanks for you report! Nice to hear it's optically good.
Im also wondering if it works like a telecentric focal extender or it's a telenegative Barlow?
I would say that it is not a telecentric, though I cannot claim that as fact. The reason I would say that is that the eye relief was clearly increased when using it with the 13 Ethos. I use the Ethos with the DioptRx accessory and I have to get in pretty close to it to take in the entire FOV so this makes me acutely aware of even very minor differences in eye relief. I have a few telecentric design barlows (TV 2" 2x Powermate, TV 1.25" 2.5x Powermate, ES 2x, ES 3x) and when using them I can tell that in use, they do not increase eye relief of the eyepiece that they are used with.
I would guess that this Luminos barlow is a 3-element apochromatic design. Being so lightweight and yielding 2.5x magnification makes me think that it is the 2" version of the GSO 2.5x apochromatic barlow, which shares the same characteristics but in a 1.25" format.