I had Two CS501 saws, good saws, very light weight.
I would not buy one to replace a 55, they are not as powerful.
But they are the only 50cc saw with a standard carb that is worth
buying.
If you want power in a 50cc saw, buy a Stihl 261, seem to be the most
reliable of the computer controlled saws out there.
I read about the new Husqvarna 550XP Mark 2 still giving reliability
and starting trouble, same for the 545, even though they use different
generation autotune, even bearing troubles, I see very little trouble with
the Stihl 261.