We started off with the Celestron 8-24mm and we were quite happy with it for the price. However we upgraded later to the Baader Hyperion 8-24mm, and now we can't go back. The things that made the difference for us are:
1. FOV, never noticed how narrow the Celestron was until now, especially at 24mm. The Baader gains ~10° AFOV across the board.
2. It's nearly parfocal, sometimes we don't even have to touch the focuser. This didn't bother us when using the Celestron, but it's actually pretty nice.
3. The click-stops. It's really nice knowing what power you're at in the dark on the fly, makes it easier to analyze and take notes which I feel helps you get more out of what you're observing.
In summary, for a fraction of the price the Celestron was a fine place to start. But if the Baader is in your budget that's what I'd recommend. If you're going to have a zoom, which is already a sacrifice in certain respects to fixed EP's, you might as well have a nice one.
I have owned a few zooms in the last years (Meade 8-24, no name 7-21 and Daytson 7-21) and i ended with the Baader Zoom Mk IV. The worst was the no name with a narrow field and poor optical quality. the Meade and the cheap Daytson were ok.
The Zoom is for me a specialized tool for planetary and doubles, but in some cases when i feel lazy, the Baader is very competitive against fixed focal lenght eyepieces in DSOs. I tend to forget the 24 mm FL and use it from 20mm to 8mm where it really excels.
I have not seen the Sbovny, but i can imagine is not far from the Baader. It could be narrower, but optically should work ok as the Sbovny line of ep´s.
After reading these two responses, I am seriously thinking about purchasing the Baader zoom MkIV. I do a lot of double star viewing/ splitting. This might come in very handy, for me.