strip you seen was the new Current Satellite LED
plus flex strip. I have two 24" Current Sat Plus fixtures (not the flex strips) and absolutely love them. They have white daylight LEDs (6500k) along side the RGB diodes. RGB chips are good for color enhancement and for complimenting all white LEDs by adding a subtle extra reds, greens, and blues for a "full spectrum" effect. This is beneficial for plant growth and color reflection in plants and colorful fish. Probably the light strips you seen on eBay are for all RGB lights, these will be very low in PAR (photosynthetic available radiation) and won't really benefit plants without a higher PAR fixture to work along side it.
Finnex makes budget friendly LED
fixtures for growing plants. Or the Current fixtures I mentioned earlier would be nice but are more expensive...