I haven't used convolver myself, but there's quite a bit of info on the author's website
http://convolver.sourceforge.net/index.html. You can check the REW exported impulse responses by re-importing them and viewing them in REW. You can even play them directly in media player or similar, though generally there won't be anything usefully audible in them - if you made a file of a large number of 1kHz filters with 15dB gain and very high Q (50, say) then exported that impulse response and played it you would hear the ringing of the 1kHz tone in the impulse response, just for curiosity's sake.