That set of eyepieces is actually a good fit for that telescope. They aren't the best eyepieces, but the focal lengths are good.

• 20mm: a bit pointless to have, but would essentially replace the 25mm Plossl. By buying the set, you basically get one eyepiece for free, so consider this one your freebie, hence why it doesn't matter if it's not that useful.
• 15mm: very useful. This would be a good general purpose deep sky eyepiece as it produces roughly a 2mm exit pupil in the F/8 scope. This balances view brightness with magnification for most DSOs. You can add or decrease magnification as needed, but an eyepiece that gives a ~2mm exit pupil is a good place to be.
• 9mm: best in the line. Very sharp on-axis. Much wider and more comfortable field of view than the 10mm that comes with the scope. I would absolutely replace the 10mm with this eyepiece. Just note that it has some quirks. There are contrast issues on the Moon and some annoying kidney beaning. As long as you're not expecting perfection, it's a great value. At 133x, this is a good conservative lunar/planetary eyepiece, and can also be used for smaller brighter DSOs (certain galaxies, globular clusters, planetary nebulae).
• 6mm: probably the weakest in the line (at least in an F/8 scope like yours, where the 15mm and 20mm will perform adequately). The 6mm gives you 200x magnification which is good for higher power lunar/planetary observing when the atmosphere is steady. The 6mm's on-axis sharpness isn't the best and contrast and kidney beaning is worse than the 9mm, but again, there aren't many options in this price class.

The 2x barlow also gives you some filler focal lengths:

• 15mm + 2x barlow = 7.5mm = 160x. This might be a great "in-between" eyepiece between the 9mm and 6mm for nights when the atmosphere can support more than 133x, but not quite 200x.
• 9mm + 2x barlow = 4.5mm = 266x. On some rare nights you'll be able to go even higher than 200x, and this would be a good combination to have. You could also barlow the 10mm for 240x. While the difference between 240x and 266x isn't huge, it might be beneficial in some cases.

I would also consider adding a 32mm Plossl. A 32mm Plossl gives you two things:

1. The widest possible true field of view in a 1.25" eyepiece
2. A relatively bright 4mm exit pupil, which is useful for pairing with nebula filters (UHC/O-III).

In another comment /u/UnityLover2 mentioned the Svbony 7-21 zoom. This is a decent alternative to that set of Svbony gold lines, but I would still pair it with a 32mm Plossl. I own the Svbony 7-21 zoom and while it has quite a narrow field of view at longer focal lengths, it is quite sharp and reasonably contrasty. It can also be purchased relatively cheaply. Here it is with a 20% off coupon: https://www.amazon.com/SVBONY-Telescope-Accessory-Astronomic-Telescopes/dp/B07Z64NK65/. Combine that with the 2x barlow you already have and a 32mm Plossl, and that's all the focal lengths you need. Again, the only downside to the zoom is the very narrow apparent field of view. It's narrower than your 25mm and 10mm Plossls at the longer focal lengths, and only smidge wider than the Plossls at the shorter focal lengths. It will be up to you if the lower price is worth the loss of the field of view.