I bought a BuzEyePro booster last winter but it didn't really work for me like I had hoped. I had hoped to use it to spot bullet holes at 200 yards for load development then use scope sans booster for varminting.
It is the 3x Multi-Coat in the Universal housing (slip on) so it wasn't one of the cheaper models, it was over $200 by the time I got it. (wish I had waited till SakoAlberta carried them

)
However, when the booster is installed I have to turn the eye focus on my scope nearly all the way in (losing magnification in scope) to focus clearly. Without it on I can back the eye piece focus adjustment out a fair bit and keep focus (gaining a bit of magnification that way). With the booster I do gain magnification but lose sharpness of image so I actually see bullet holes better without it most days.
If you get one I would recommend the 4x with Multi-Coat
Slightly more costly but the way the optics work the 3x has less effect than I expected, (I estimate 10% increase).
Maybe a better scope would respond to the booster more favourably than mine (Leopold VX-II 6-18x40) and retain image sharpness with it on.
I am not saying the product does not work!!
Just not as well as I had hoped. Hope to try it on other scopes to see if I can find a place for it before I give up and sell it on EE.