The basic limitation of either Raynox closeup lens is the working distance. The DCR-150 is +4.8 dioptre with a working distance of about 6-8in / 150-200mm. The DCR-250 is +8dpt with a WD of 5in / 125mm. Those stay the same NO MATTER THE FOCAL LENGTH OF THE HOST LENS. The magnification obtained from these or any other +dioptre closeup adapter is given by:
M= F*D/1000 where F is focal length in mm and D is dioptres
So the DCR-150 on a host lens set to 30mm gives (30*4.8=144)/1000= ~1:7 which ain't very macro at all. For the DCR-250 it's (30*8=240)/1000= ~1:4. Neither Raynox gives useful magnification at short focal lengths. Also, the DA18-55 has a close focus of about 8in / 200mm which is in the DCR-150's range, so it doesn't even provide much in the way of close-ups.
What's the optimum focal length for a DCR-250's host lens? As
Verglace said, it's around 100mm. The DCR-250 on a 135/2.8 host lens would have ~1:1.1 magnification at the same working distance as a 135mm lens on sufficient extension.
How do such adapters compare to dedicated macro lenses? A macro lens will have a bit better IQ and a greater range of working distances than will a lens with a Raynox attached. But the Raynox is easily detached for non-macro shooting, so its main inconvenience is just the limited working distance.
A big Raynox advantage is that it doesn't eat light. A fully-extended macro lens loses 2 stops of light compared to the same lens at infinity focus (zero extension). A Raynox or other +dioptre lens actually boosts light a little.
The Raynoxi are graet -- just take their limitations into account.