Markus Ludes (the russian telescope importer) did a test about a month ago on barlows and found that they all were pretty much the same (my opinion) for quality of the optics. The 2.5X will give you a little more magnification but putting it in with the 2X will boost even more. Unless the Barlow that you have is really bad, you probably won't see a difference with the new barlow. That's my opinion. That and a buck gets you a cup of coffee.