Welcome aboard. Essentially the image quality from the C.I. is the equivalent to an HTPC. However, since "HTPC" is a generic term and the C.I. is a specific component, it's a bit of an apples/oranges comparison. Having owned a C.I. for about 4 months, I can tell you that I'm very pleased with the image. In my instance, I went with the C.I. rather than an HTPC because I view multiple sources other than DVD (i.e. LV, DISH, S-VHS, etc). At this point these sources do not look good when routed through an HTPC.
Keep in mind that these are both 'cutting edge' approaches to getting a great looking signal to your projector. Both require some patience. Based upon my own experience, and reading posts on this forum, I would not describe either approach as "plug and play". The DVDO iScan IS "plug and play" but yields nowhere near the picture quality of the Crystal Image Scaler.