Hi, i have a SX40 and a Polaroid 4 lens kit and i just got a Raynox 250, (haven't had the oportunity to test the raynox outside yet)
What i can tell you is that the SX40 is very capable without a macro attachment, but if you have a macro lens, it will help make it even better, now the problem with cheap lenses (like the Polaroid 4 lens kit) is that the quality is not the best at high magnification (+4 and +10 diopter), you get alot of chromatic aberration as you can see in these examples below:
but on the lower diopters (+1 and +2) it is practically inexistent and these are very useful to get macros from far away as you can see in the next example:
(on the wide angle you can see vignetting because both the polarizing filter and the close up lens were attached, if the polarizing filter wasn't on there wouldn't be any vignetting even at wide angle, these are 67mm lenses)
Right now i have a Raynox 250 to substitute the polaroid high diopter lenses, from what i've tested on "not living" subjects (toy cars and such) the quality is much superior to the polaroid ones, there are no chromatic aberrations and the quality of the photos comes out much sharper than the polaroid, it does have alot of vignetting at wide angle but those macro attachments aren't supposed to be used at wide angle anyway so as soon as you start to zoom in the vignetting starts to disappear, as soon as i get some proper shots i will post it on "My SX40 works" thread.