reliability of historical data in mt4

Does anyone know how reliable is data available in the history center of mt4 when you use the download feature? I searched the threads and found few threads on improving the model quality of mt4 tester. Posters said that alpari databank contains reliable 1 minute data (for EURUSD) since 16 june of 2004. I dont really need 1 minute data, 30 minutes will suit me well. Is 30 minute data downloaded in history center reliable?

Alpari's data is fairly reliable in anything above the 5mins chart. I wouldnt trust much the 1min data though.

What about when you hit the download button in history center. The data comes from MetaQuotes Software Corp. How reliable is that data? I am looking for 30 minutes reliable data since say 1999.