I have previously owned a similar device (The Digital King 0.7x version, which is also a budget wide angle adapter but a fair bit more expensive than the one you've linked). In fact I used it for exactly the same thing as you. For website house rental photos I thought it was fine, those photos aren't meant to be works of art and they are only used for a few weeks. I suppose if it's a very high end rental I may have wanted to use something with a little more quality.

There is a significant amount of softening near the edges though, as well as some barrelling. This didn't bother me for the rental photos, but I wouldn't want to use one for an 'arty' photo. I have a comparison on Flickr somewhere, I'll dig it up for you.

Edit: here you go:


DA18-55@18mm - complex by thoughton, on Flickr


DA18-55@18mm + 0.7x converter - complex by thoughton, on Flickr

You're on my friends list, so you should be able to click through for full size 6 megapixel versions (these photos were taken 2 cameras ago )

Note the curved shed, and very soft extreme corners.