Difficult questions about expert advisors

 
Hi friends!
I wounder how to test whether different EA could work on same platform and account.Also i would like to understand why some EA smiles but did not work - no trade.And last question what is the difference between visual mode and no visual mode in strategy tester,which one is more precious .What about expectancy - future performance of EA.Is this topic worth http://www.tradingmarkets.com/.site/forex/how_to/articles/How-to-Find-the-Best-MetaTrader-EA---Part-1-81004.cfm
I hope somebody to have good answers.
 

i would imagine if the EA smiles but did not work there must be something wrong with its trading strategy, maybe you might find in the log file some indication to what it was doing.