I purchased the Celestron X-Cel LX 3x barlow to give it a try. I wouldn't argue with your point, N3p, that this is often too much power. For my 10mm BCO, I tend to agree with your assessment. It's rare in my skies, that they'd support a 3.33mm-simulated eyepiece in most of my scopes. Possible, especially on a target like the moon, but for most things, even double stars that require a steadiness in atmospheric cooperation, rare, indeed. However, with a 3x barlow, eyepieces like my 20mm or 17mm Long Perng Plossls, or an 18mm BCO (which I might pick up to check out), begin to have planetary implications they otherwise would not possess. The 3x barlow opens up that realm in the medium to low power eyepieces. One must be careful with this. Barlows tend to increase eye relief, and with something like a 25mm plossl, the eye relief can render the eyepiece-with-barlow prone to blackouts. But in the 20mm and below sizes, they can become planetary contenders that they otherwise wouldn't really be. 9mm is good, but 6mm is planetary, and, of course, 18mm is not, so a 3x barlow can have a place in the eyepiece case. And it's always there should the Sky Godesses unveil their heavenly bodies and allow sub 5mm-equivalent-barlow-combos to reveal their celestial glories. Always ready. The 3x barlow, kind of like a condom.
I have to agree with that in red.