The Solo 633? I just got done testing a modified one for a week. It is comparable to the Echo 340. Power-wise, the modified Solo was about dead even with my Echo (I've modified/ opened up the muffler on my Echo) but had a little less vibration. Weight was about the same, both total weight and nose weight. I was concerned about the durability of the air filter which was just a cut out piece of cloth with another cut out piece of foam over it. The Echo has a durable rubber frame on the air filter.
Parts may be hard to come by, as Solo doesn't have a very good distribution system throughout the US. The bar is also not a standard bolt pattern so you will need to order extras when you find a source. Not every corner saw shop will have a bar, unlike the Echo.
Overall, I was fairly impressed with the quality of craftsmanship in the saw for as inexpensive as they are. More power would have been nice but lack of a close parts supply tilted the scales against it for me.
Before others bring it up, both the Solo and my Echo were about 25% slower in the cut than a stock Stihl 020T. (But I can disassemble and reassemble the throttle linkage in the handles of the Solo and Echo).