The Lower power eyepiece (25MM) gives you both a wider field and sharper images. It's less magnification. You get the magnification by diving the focal length of the eyepiece by the telescole. 910 / 25 = 36x. Or 910 / 10 = 91x. The Barlow lense will double the magnification. So with the Barlow and the eyepieces together you would get 72x and 182x. I bought one. Hardly ever used it. I only used it with the 10MM when looking at the planets and Moon. A smaller eyepiece would have accomplished the same thing and be better. Remember, at high magnification you loose some brightness and clarity. For most objects a smaller clearer image is preferable, especially with the deep sky stuff. I used that scope mostly with the 32MM Teleview at 28x. Real nice stuff. Three eyepieces small, medium and large are all you really need. You can get as many as you like, but you'll have one or two favorites, so it's best to get a few good ones over many cheaper one to get a wide range. Belive me, things don't look that much different at 110x than 90x. Let me recommend you start reading Astronomy or Sky and Telescope magazine. They give you all the information you need on accessories and what to look at. Get a good starter book also. The biggest problem with new people in this hobby is over-anticipation. Your not gonna see anthing like the pictures in the magazines. Those are mostly taken with huge telescopes and very long exposures. Saturn will look outstanding. Jupiter will be large and all 4 moons are visible but the details on the planet will subtel. Galaxies will look like faint smudges. Globular Glusters will look like cotten balls with maybe a few stars resolving on the edges. Open cluster will look very nice with many stars all together in one place. Nebulas will look like clouds and Planetary nebulars come in all shapes and sizes, but all will be subtel. Your not gonna see color except in the different color stars, again subtel differences. Keep me posted. Just trying to give you a realistic impression of what to expect.
That's it;
BOB SAL