The relay thing is there to add load. Modern LEDs draw so little power that they don't put the proper load on the flasher for them to work right. There are special flashers that work right with the low load LEDs, but if you don't use one then (you don't know what you are doing or have some special case) you need to fake the load for them to work right.
There are a LOT of LED kits out there. Many very poorly designed with no correct engineering to how an original light actually works. For example an original 1157 tail light bulb shines in all directions. The housing reflects (often poorly) that light toward the rear. Add in the Fresnel lens of the tail lamp and you have a nicely engineered light. Toss in a POS LED that has a handful of LEDs that shine straight out, you just lost all that reflected area and the function of the fresnel lens. Yea it functions, but nowhere near as good as it could. It just has a hot spot dead center with a little random scatter of light. Speaking of heat, LEDs don't like it. I have seen a few LED conversion bulbs that chunked out the potting. LEDs are great for low power applications. Once the wattage starts going up, heat disipation becomes an issue.
$55 your cost? WOW that has got to be some very special light (or more then likely going through too many middle men and has too much profit margin). I have bought some LED lights and full retail was never as high as $55 each.
