I've been using this ocular for years on my Questar 3.5. In fact I rarely use the Brandon oculars (16 mm and 24 mm) which came with the telescope. I am not a particularly skilled observer but for my purposes this ocular is fine: sharp edge to edge, no visible aberrations, and, very important for me, great eye relief (15 mm, which allows me to use it while wearing my astigmatism-correcting glasses).
The only problem is that its entrance plane is a little deeper inside the tube than the telescope is designed for. But I was able to fix that by fabricating an adaptor that mounts the Vixen right up against the Questar control box, making the main tube parfocal (approximately) with the finder.
Bottom line: no need to carry any other ocular when you go outside with your telescope if you have this mounted.

I put in a comment to the other evaluation, but then decided to make this a formal review, so the eyepiece is not frozen at a low rating.
We all seem to agree this is a fine eyepiece, but relatively (the key word) expensive - after all, Vixen is competing against the low wages of Communist China. With a little experience, you can tell why Vixen is still in business, though. The Celestron eyepiece is adequate for introducing the deep sky, but that's it. I use this eyepiece all the time, the only exceptions being solar, lunar and planetary when the seeing is particularly good and the Brandon eyepieces - in a Baader turret - show their stuff, and also when the deep sky object is particularly elusive and I then put in the Vixen 40 mm Plossl for scanning. Otherwise, a good zoom is great - you can, first, FIND the object and then choose the optimal power for the details (it has recently been shown that amateurs have not been using enough magnification on these faint objects to obtain optimum contrast). Someday maybe I'll spring for a Televue or other truly high-priced eyepiece, but not today - not ready for a genuinely serious outlay.

I have bought this Vixen Zoom eyepiece to upgrade from my standard Celestron Zoom one. I was very disappointed. The eyepiece functions perfectly, please, do not take this review as negative. There is nothing wrong with the unit from the optical point of view. However, price is more than three times more expensive than the Celestron comparable zoom, and about six times than the cheaper imitations from China.

The Celestron unit performed identically for my eyes. Maybe someone who measures different outputs of the lens may notice some statistical difference in performance, but my normal human eyes could not tell one lens from the other.

You can buy the Celstron zoom eyepiece for about 60 bucks and save the rest for enough beer or coffee during your sky exploration nights.

Alternatively, if you just have a play telescope for your younger kids, just go ahead and buy the 35 dollar Zhumell eyepiece and upgrade later, if you ever get to keep their interest and they require a bigger scope with better optics.