I purchased a CS501p and CS620pw 2 years ago. Pulled the carb plugs and did muffler mods as soon as I received them. I'm very happy with both, but particularly impressed with the 620. That thing pulls like a tractor. Easy to start, runs great, extremely happy with it.
I managed to blow up my 501 a month or two ago, messing with the carb and being inattentive. OEM cylinder was $94, piston kit was mid $40s, etc. I thought those prices were reasonable for OEM items.
I'm very happy with my decision to go Echo vs Stihl for my "new saws". I still have (4) 028s in various states of condition. I'll be selling 3 of them, and keeping one as a back up.
Glad to know about the bar adapters. May not matter to me, but with a Stihl dealer nearby (and no Echo dealers) it may be worth converting to the Stihl bar when the Echo bars wear down.