Strengths: - Exceptionally easy to setup
- Holds it's tune well
- Very easy to disassemble the pulley cage for cleaning, quality hardware so the little bolts don't wear out
- Quality bearings on both pulleys, after cleaning they spin freely good as new
Weaknesses: If you're coming to a stop from a high rate of speed (i.e. traffic light changes in front of you on the flats or on a downhill) and you're in a very small cog, you can't safely dump gears as quickly as with Shimano deraiullers.
If you try to downshift about 6 gears very quickly the chain will jump off the top pulley and jam. As long as you stop pedaling instantly it's OK, but it requires coasting to a stop and fixing the chain. I did this 2-3 times when I first bought the Rival group and my pulley cage is quite gouged as a result, but the deraiuller did not break. Now I have adjusted my shifting style and this never happens, I make sure to downshift 2-3 gears, pedal, and then downshift another 2-3 gears.
It appears the cause of this is trimming the cage a little excessively, possibly a foolish weight saving measure.
Overall I'm fairly happy with this deraiuller. It basically only has one weakness.