I found a reliable review of the SWAN series here:
http://www.cloudynights.com/documents/swan.pdf
By virtue of the slower light cone the barlow should improve performance of the eyepieces in your f/5 scopes and provide longer eye relief than the equivalent shorter eyepiece (assuming the barlow is well made).
I can recommend the high quality Antares 2" 1.6x barlow to you - it would noticeably improve the performance of any of your SWAN eyepieces in your fast scopes - the sharp area of the field would extend further out from the center, eye relief would be extended and the low magnification factor would let you use more of your eyepieces with the barlow. It's also quite a short barlow.