You can image narrowband with achromats perfectly well, you just need to focus in between filters (no big problem, would be good practice to do so with an apo anyway).... I did the same in 2007, bought a 100mm f/5 for narrowband....
I have both an ED80 and a 100mm f/5 Skywatcher achromat, I haven't weighed them, but I doubt any weight differential would be more than 10%....
Not a bad scope really, the focuser is a bit ordinary though, to be expected for the $$....
I'd say go for it, a cheap venture in the scheme of AP! I use mine as a guidescope now (got aperture fever).... there is always the 150mm f/5 too....
