Yep Merc stealth was originally designed by Ideazon and it became a Steelseries product when they took over Ideazon. My intent in purchasing the Merc Stealth was to get a Gaming Keyboard with good back lighting so it can be used even in the dark. For a Membrane keyboard it is pretty good (No membrane keyboard lasted more than 2 years for me) and as Digital Dude pointed out the gaming area keys are not such a great help. Moreover it adds considerably to the length of the keyboard. Mine doesn't fit properly on the keyboard tray of my computer table.
I have always considered Mechanical keyboards to be the best for gaming and Black Widow adds back lighting to a mechanical keyboard along with the usual Razer bling and features making it the perfect gaming keyboard. Do note that Mechanical keyboards are very sturdy and last a very long time. I have one that is 13 years old and still in perfect working condition (except for the fact that it is based on the ancient AT Interface hooked that can only be used via a AT~PS/2 converter). So if you get a Black Widow now, unless there is a radical change in Human Computer interaction, you would be left the lamest of excuses to ever upgrade your keyboard within the next 12~15 years.
Personally I would go with the Black Widow and I am seriously considering the upgrade myself. The only thing you should look out for the tactile feedback that a mechanical keyboard has. There are people who don't like the click and the tactile feedback of mechanical keyboards.
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Just to add, only the Black Widow Ultimate has Back lighting. If you cannot afford that and still want a decent keyboard with back lighting, you can consider the Logitech G110.
