Camera sensitivity and resolution. The noisier the image, the harder it is to find and distinguish a guide star. These cameras are intended for use in lit situations, not dark. A popularly recommended first guide camera recommended is the Phillips Toucam or SPC900 (or something like that). I had one originally. It works, but the image quality and ability to consistently get guide stars is chalk and cheese with even the cheaper proper guide cams like QHY5 or Orion equivalent.
If you're serious about astrophotography, save yourself some heartache and the $30 or whatever for these cheapies and get yourself as a minimum something like the QHY5. You'll be wanting to upgrade in a short time anyway, trust me
