I put some of the eyepieces noted in the OP through their paces last night in my 16" f4.5 astrosystems dob in front of my moderately light polluted home (typical SQMs of upper 18s & lower 19s) and a bright moon at 52% illumination. Such conditions obviously pose a significant challenge although excellent transparency and good seeing helped quite a bit.
First up, the Svbony 7-21mm zoom eyepiece. As noted in the review by Ernest, this inexpensive zoom actually has quite good image quality and apparently better than other and more expensive zoom offerings in the Svbony line:
I checked the appearance of Arcturus and Jupiter at various settings and noted some chromatic aberration near the edges but, overall, the images were clean and nearly parfocal through the focal ranges. After further observations of the limb of the moon, I believe the chromatic aberration seen was actually due to the objects being relatively low in elevation and likely caused by refraction of the earth's atmosphere. This is a very comfortable zoom eyepiece to use for a non eyeglass wearer like myself with 16-18mm or so of eye relief with the eyecup up. The AFOV is relatively small, as noted in the review by Ernest, but that didn't seem to detract from the view as I tracked Saturn at the 7mm setting. I was able to pick up a moon close to the globe at the 7mm setting that I couldn't see in my 10mm Ethos because of the increased magnification needed and also because of the increase in contrast necessary to overcome the brightly lit moon. I have no doubt that the Ethos would have picked up the moon in close proximity of the planet had our own moonlight not been present. To further ratchet up the tension and increase the challenge, I observed NGC 404, the 10.3 magnitude galaxy in Andromeda that can be difficult to see due to the brilliant glare of the second magnitude star, Beta Andromedae, adjacent to it. I found I could see it fairly well at the 15-17mm settings after failing to detect it at the upper and lower settings. I did find, however, that the 10mm Ethos did offer a better view of it than a similar focal length setting on the zoom. Overall, the contrast was better in the Ethos and I felt the same in comparing the 7-21mm zoom to its other stablemate in my eyepiece case, that being the 3-8mm zoom. I viewed Saturn through of all of its settings and I was quite impressed with the image, particularly at the 3mm range although Ernest pegs it at 3.5mm but I'm using a paracorr so that drops it back below that level. The more I use the Svbony 3-8mm zoom, the more impressed I am with it. I find both of these zooms superior to the 8-24 wider field Svbony zoom in my collection and better than the Zhumell 8-24 Celestron clone zoom that I've owned for years.
Next up: the Celestron 15mm spotting scope eyepiece. I'll cut to the chase, at 12 bucks, this is a steal, period. If you can find a better 15mm eyepiece at several times the price, buy it! I viewed no less than five galaxies last night through it despite the presence of a brilliantly lit moon and the ambient light pollution. NGC 404 was readily seen as were NGC 7331, 7332 and it close companion 12th magnitude 7339 (with averted vision) and 1023. With about 18mm of eye relief and a wider than advertised AFOV of around 60 degrees, this is a very comfortable eyepiece to use. Starman1 pegged the AFOV of this eyepiece at 65 degrees while viewing through it in my scope up at Mt Pinos earlier this month. Neither one of us used a drift method or similar so these are estimates but the AFOV won't leave you wanting in the 1.25" eyepiece range. Overall, nice contrast, and better than a 15mm Svbony 68 degree AFOV Orion expanse clone and equivalent that I have in my collection. (The 9mm eyepiece is the best in that particular series, in my opinion.) The Celestron 15mm spotting scope eyepiece: I can't see how you can go wrong with this eyepiece.
Next up: the Svbony 34mm wide angle 2" eyepiece. As Jon Isaac has noted, this is actually a 32mm equivalent to the Orion 2" model. Even at f4.5, with a paracorr, the AFOV is reasonably well corrected and even better in a longer focal length instrument. Although I paid about $39.00 for mine on ebay several years ago but at its sale price of around $54.00, you're still getting a heck of a deal. Very comfortable to use with a wide expansive field of view. I think it's an excellent eyepiece for novice observers...