You will NOT get vignetting with either Raynox. I use the DCR-250 on my DA18-250 with 62mm front thread, no problem. The Raynoxi will mount on lenses up to 69mm thread. Note that the DA18-135 close-focus distance (unaided) is ~400mm.
CORRECTION: I goofed. I *do* see vignetting with the Raynox on my DA18-250 -- I was thinking of my FA100-300 instead. Now I remember why I got that 62mm +1+2+4 dpt closeup set for my wider-objective lenses. I heartily apologize. Please ignore the following advice about using Raynoxi on the DA18-135.
What's important are the characteristics of the Raynoxi, which are +dioptre achromat (corrected) optics. They shorten the focus distance to the same range no matter what focal length the host lens. Here are their strengths and focus distances:
DCR-150: +4.8dpt, ~170-210mm
DCR-250: +8.0dpt, ~125mm
To calculate magnification:
M = F*D/1000 where M is magnification, F is host lens focal length, and D is dioptre of the add-on lens. So with the DA18-135 zoomed out to 135mm and set to far focus, the magnifications for the Raynoxi are:
DCR-150: 135*4.8/1000= ~0.65x
DCR-250: 135*8.0/1000= ~1.1x
So if you want less magnification and a greater working distance, get the DCR-150. And if you want more magnification and a closer working distance, get the DCR-250. You can also increse magnification and decrease working distance with either by adding 49mm close-up optics (the kind sold as +1+2+3 or +1+2+4 dpt sets for a few bucks) to the front of the Raynox. Have fun!