I have an echo CS 352. I like it- it's light and starts super easy, even easier than I'd expect a 34cc saw to start.
The air filter is not as good as the Stihl filters in their M-tronic saws. It lets some fine material into the carb. I stuffed some oiled foam filter material in the air box to try to trap some before it gets to the filter. The gas and oil filler holes are small so its easier to overflow. The saw came with the carb adjusters set as rich as the limiters allow and it was still a little lean. I removed the limiters, trimmed the tabs and put them back, then adjusted to spec using a tach. I also removed the catalytic converter but left the muffler stock otherwise because it's quiet.
If it was me I'd try to figure out what's wrong with the 550. Many problems like that are fixable. It might just be a carb that needs cleaning out. Is it unusually easy to pull over? The rings may just be worn so much that it doesn't have enough compression.