The short barlow (at least standard quality) has the shorter focal "relief" for a good reason. The longer barlows can be used IF the telescope's focuser, let alone focal ratio, will accept it. Example. If I were to use a standard barlow on a Fast newtonian like a f/5 or f/4.5, it would work well for one thing because the focus plane would be to high or (low) and you couldn't focus well. The standard barlows do work well on long focal length refractors like a f/9 on up. The shortys were designed to eliminate the hassle and threat of not working on certain newts and SCT's for that matter. It's just plain good sense to have a shorty barlow handy. They work on just about everything. They are also great for "negative" projection photography. Most good seasoned amateurs will say to get a shorty barlow. Even some of the variable barlows (most are short too)are fast becoming good investments. Orion's Shorty Barlow is a good Barlow as is a few others. Tele-Vues Powermate series are all basically short. These shortys don't degrade the view that much and it doesn't "harm" the eye relief as well.