Extended ROM is typically the hidden rom used by the Brand who is selling the device to put their custom stuff on the device, but it is also where the device manufacturer puts device finctions that are very necessary for the devices operation and functions of embedded programs/systems.
Up until I recently heard the Magician's ExtROM is different then the last few devices made by HTC, the ExtROM was hidden, but the gurus on this site created tools to unlock and make the ExtROM useable fr5om a read/write perspective. The Himalya and Blue Angel have ExtROM unlocking tools, which allows you more storage and the ability to install applications you want in this memory area, and you can delet those sometimes redundant and silly custom parts of the ExtROM placed their by the Brand Seller.
Access to the ExtROM on the Magician would be golden considering the limited memory. In my case I had PPC Techs crank my RAM up to 128 so I'm ok.