The Raynox 150 is terrific on the 55-300mm. Just set the lens for infinity focus and use the zoom to go from about 1:2 macro all the way to 1.4:1. You won't notice any significant difference in quality with the Raynox mounted vs the lens by itself. I would stay away from simple close-up lenses. The photos I've seen with simple macro lenses have exhibited excessive purple fringing and a loss of sharpness.
Achromats are a step up in quality compared to simple macro lenses, for a similar price. The Raynox is a multi-element lens with achromatic correction, as is the Canon 500D. The 58mm Canon will screw directly onto the 55-300, the Raynox comes with an adapter that fits any lens from 52-67mm filter size. Or you can screw the Raynox out of its adapter and mount it in a stepped ring, so it screws into the filter threads. I can't find a spec just now, but I believe the Raynox 150 has slightly higher magnification than the Canon.
Check out this thread:
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/74221-raynox-macro-club.html