I have a cheap Truvativ Touro compact crankset that is 36/50 and an 8 speed drive train. I was looking at replacing the 36T chainring with a 34T so I started looking around. It looks like the cheap end of the chainrings are usually around $30 with one exception. This Ultegra 34T chainring is only $13.

I was under the impression that Ultegra is usually quite good, am I missing something as to why it's that cheap? Is there a compatibility issue or something? Thanks.