See
http://www.televue.com/engine/TV3b_p...k#.U6PNSJSSy5I regarding Powermates versus Barlows.
Powermates are not cheap but they perform very well. Note though that the 2x Powermate is only available in 2" size and is heavier than a 2" 2x Barlow (although not as heavy as the 4x). The 1.25" 2.5x Powermate would be ideal for 25mm eyepieces upward to avoid giving you eye relief that is too long. Can also be used for eyepieces under 20mm to give you quality high power viewing through eyepieces that have a larger eye lens making it much easier than those pin hole 6mm and under Plossl eyepieces.
Note the very early 2.5x Powermates were not threaded for filters but the current new ones are. I'm not sure which year the change was made.