There IS no way to keep up unless you actually use these different units. You certainly cannot tell by reading their advertised specs.
Yes, I've got many cheap Cobra, Vectors, Harbor Freight, Duracell, AIMs, etc. and all work fine for most things. None will run a GFIC outlet of a smoke alarm though. That's an issue when wiring a low voltage house and trying to pass inspection.
So, I HAD to buy this $800 "true sine wave" inverter to pass inspection. My 4000 watt hard-wired Trace/Xantrex would not pass since it cannot run the smoke alarms and GFICs. Note that this new unit runs the required stuff perfectly but will NOT run an 18 volt charger. It comes on but never shuts off. I left one on for two full days. Then stuck it on a cheap mod-wave Vector and it got done in 15 minutes.