Sorry to bump this, but I've been running Rossi engines for almost 5+ years. I don't have anyone of the on engines listed above but I will say they last a long time. After 5+ years my Rossi .21 ECO still has good compression. I used it in a project AE RC10GT car that was able to propel it to 71mph. Anyhow, I just purchased a AXE Cobra the other day and hopefully they still have what they had years ago quality and longevity.
I think the biggest thing with any engine is the critical part of breaking it in. I think most of the problems people have with their engines is the fact they don't take the time (eg. get into the mindset) that this is a very critical part of the engines life.