Glorystar receivers have some customizations in their firmware (or so I have read). You can upgrade your MercII with firmware from the manufacturer, but you'll lose any of the features that Glorystar has in store for your receiver (like automatic channel mapping and possibly EPG functionality?) when they release that functionality.
If you're going to upgrade, I'd keep a copy of the currently loaded firmware so that you can go back incase Glorystar releases changes that you would really like. Other than that, the only other issue I see is that some manufacturers will not support your warranty if you've flashed your receiver with different firmware, so you might check your warranty first.