Let me say right off the bat that Logitech's G512 SE is not in contention to be crowned the absolute best gaming keyboard, because it lacks some of the amenities that higher-end models offer. But for $49.99, as it is currently priced at Best Buy, it is one of the best values in the mechanical keyboard space.
Our favorite mechanical keyboard, Corsair's K95 RGB Platinum, costs more than twice as much for a refurbished model, and more than three times as much for one that is brand new. Like most things, you get more if you are willing to pay more. So, what do you get with the G512 SE? A value driven alternative that doesn't suck.
Value is sometimes code for piece of junk, though that is not the case here. The frame on the G512 SE is made of an anodized, brushed aluminum-magnesium alloy. Logitech claims it is "aircraft grade," but we've never parted out a keyboard to build an airplane and don't suggest you try it either.
The version that is on sale also uses Logitech's GX Blue key switches. These are clicky (read: loud) and tactile, similar to Cherry MX Blue switches. I'm a fan of blue switches myself, but if you prefer quiet and/or linear switches, you should wait and see if one of those models go on sale (the G512 SE is also offered with GX Brown and Red switches, but the cheapest price elsewhere is $99.99, direct from Logitech).
You don't get features like dedicated gaming keys or a fancy LCD, but this is not a completely barebones mechanical keyboard. It offers customizable RGB backlighting that you can synchronize to games and other content via Logitech's Lightsync technology, and USB pass-through. Not bad for a $50 plank.
As far as I'm aware, the last time this keyboard sold for this price was last December. Best Buy lists the normal price as $149.99, but it's really a $99.99 plank, which I think is a little high. At its current discount, however, it's a better buy than Logitech's K840, our top choice for gamers on a budget.